[performance] bump codeberg.org/gruf/go-kv to v2 (#4341)

updates our codeberg.org/gruf/go-kv log key-value formatting library to latest version, which comes with some maaaaaaajor speed boosts in the form of:
- very minimal reflect.Value{} usage
- caching prepared formatting functions per type

~~still a work-in-progress until i make a release tag on the go-kv repository, which itself is waiting on published benchmark results in the README and finishing writing some code comments~~

benchmarks so far show this to be ~3x faster than the "fmt" stdlib package on average, when run across a wide variety (106 different types) of test cases, while still creating more visually friendly log output and actually recursing down nested struct ptrs

Reviewed-on: https://codeberg.org/superseriousbusiness/gotosocial/pulls/4341
Co-authored-by: kim <grufwub@gmail.com>
Co-committed-by: kim <grufwub@gmail.com>

vendor/codeberg.org/gruf/go-kv/v2/README.md

@@ -0,0 +1,5 @@
+# go-kv
+
+This library provides a key-value field structure `kv.Field{}` that plays well with the `"fmt"` package. It gives an easy means of appending key-value fields to log entries, in a more performant manner that also happens to look nice! (it's not far removed from using a `map[string]interface{}`).
+
+The formatting for these key-value fields is handled by the `"fmt"` package by default. If you set the `kvformat` build tag then it will use a custom formatting library found under `format/`.