[feature + performance] add JSON logging format (#4355)

# Description

Adds JSON logging as an optional alternative log output format. In the process this moves our log formatting itself into a separate subpkg to make it more easily modular, and improves caller name getting with some calling function name caching.

## Checklist

- [x] I/we have read the [GoToSocial contribution guidelines](https://codeberg.org/superseriousbusiness/gotosocial/src/branch/main/CONTRIBUTING.md).
- [x] I/we have discussed the proposed changes already, either in an issue on the repository, or in the Matrix chat.
- [x] I/we have not leveraged AI to create the proposed changes.
- [x] I/we have performed a self-review of added code.
- [x] I/we have written code that is legible and maintainable by others.
- [x] I/we have commented the added code, particularly in hard-to-understand areas.
- [x] I/we have made any necessary changes to documentation.
- [ ] I/we have added tests that cover new code.
- [x] I/we have run tests and they pass locally with the changes.
- [x] I/we have run `go fmt ./...` and `golangci-lint run`.

Reviewed-on: https://codeberg.org/superseriousbusiness/gotosocial/pulls/4355
Co-authored-by: kim <grufwub@gmail.com>
Co-committed-by: kim <grufwub@gmail.com>

vendor/codeberg.org/gruf/go-caller/LICENSE

@@ -0,0 +1,9 @@
+MIT License
+
+Copyright (c) gruf
+
+Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

vendor/codeberg.org/gruf/go-caller/README.md

@@ -0,0 +1,3 @@
+# go-caller
+
+runtime-cached Go calling function names per PC, useful in shaving time from outputting log entries.

vendor/codeberg.org/gruf/go-caller/caller.go

@@ -0,0 +1,136 @@
+package caller
+
+import (
+	"runtime"
+	"strings"
+	"sync/atomic"
+)
+
+var (
+	// callerCache caches PC values to string names.
+	// note this may be a little slower than Caller()
+	// calls on startup, but after all PCs are cached
+	// this should be ~3x faster + less GC overhead.
+	//
+	// see the following benchmark:
+	// goos: linux
+	// goarch: amd64
+	// pkg: codeberg.org/gruf/go-caller
+	// cpu: AMD Ryzen 7 7840U w/ Radeon  780M Graphics
+	// BenchmarkCallerCache
+	// BenchmarkCallerCache-16         16796982                66.19 ns/op           24 B/op          3 allocs/op
+	// BenchmarkNoCallerCache
+	// BenchmarkNoCallerCache-16        5486168               219.9 ns/op           744 B/op          6 allocs/op
+	callerCache atomic.Pointer[map[uintptr]string]
+
+	// stringCache caches strings to minimise string memory use
+	// by ensuring only 1 instance of the same func name string.
+	stringCache atomic.Pointer[map[string]string]
+)
+
+// Clear will empty the global caller PC -> func names cache.
+func Clear() { callerCache.Store(nil); stringCache.Store(nil) }
+
+// Name returns the calling function name for given
+// program counter, formatted to be useful for logging.
+func Name(pc uintptr) string {
+
+	// Get frame iterator for program counter.
+	frames := runtime.CallersFrames([]uintptr{pc})
+	if frames == nil {
+		return "???"
+	}
+
+	// Get func name from frame.
+	frame, _ := frames.Next()
+	name := frame.Function
+	if name == "" {
+		return "???"
+	}
+
+	// Drop all but package and function name, no path.
+	if idx := strings.LastIndex(name, "/"); idx >= 0 {
+		name = name[idx+1:]
+	}
+
+	const params = `[...]`
+
+	// Drop any function generic type parameter markers.
+	if idx := strings.Index(name, params); idx >= 0 {
+		name = name[:idx] + name[idx+len(params):]
+	}
+
+	return name
+}
+
+// Get will return calling func information for given PC value,
+// caching func names by their PC values to reduce calls to Caller().
+func Get(pc uintptr) string {
+	var cache map[uintptr]string
+	for {
+		// Load caller cache map.
+		ptr := callerCache.Load()
+
+		if ptr != nil {
+			// Look for stored name.
+			name, ok := (*ptr)[pc]
+			if ok {
+				return name
+			}
+
+			// Make a clone of existing caller cache map.
+			cache = make(map[uintptr]string, len(*ptr)+1)
+			for key, value := range *ptr {
+				cache[key] = value
+			}
+		} else {
+			// Allocate new caller cache map.
+			cache = make(map[uintptr]string, 1)
+		}
+
+		// Calculate caller
+		// name for PC value.
+		name := Name(pc)
+		name = getString(name)
+
+		// Store in map.
+		cache[pc] = name
+
+		// Attempt to update caller cache map pointer.
+		if callerCache.CompareAndSwap(ptr, &cache) {
+			return name
+		}
+	}
+}
+
+func getString(key string) string {
+	var cache map[string]string
+	for {
+		// Load string cache map.
+		ptr := stringCache.Load()
+
+		if ptr != nil {
+			// Check for existing string.
+			if str, ok := (*ptr)[key]; ok {
+				return str
+			}
+
+			// Make a clone of existing string cache map.
+			cache = make(map[string]string, len(*ptr)+1)
+			for key, value := range *ptr {
+				cache[key] = value
+			}
+		} else {
+			// Allocate new string cache map.
+			cache = make(map[string]string, 1)
+		}
+
+		// Store this str.
+		cache[key] = key
+
+		// Attempt to update string cache map pointer.
+		if stringCache.CompareAndSwap(ptr, &cache) {
+			return key
+		}
+	}
+}