[feature] update proof-of-work to allow setting required rounds (#4186)

# Description

This updates our proof-of-work middleware, NoLLaMas, to work on a more easily configurable algorithm (thank you f0x for bringing this to my attention!). Instead of requiring that a solution with pre-determined number of '0' chars be found, it now pre-computes a result with a pre-determined nonce value that it expects the client to iterate up-to. (though with some level of jitter applied, to prevent it being too-easily gamed). This allows the user to configure roughly how many hash-encode rounds they want their clients to have to complete.

## 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/4186
Co-authored-by: kim <grufwub@gmail.com>
Co-committed-by: kim <grufwub@gmail.com>

vendor/codeberg.org/gruf/go-bitutil/abs.go

@@ -0,0 +1,29 @@
+package bitutil
+
+// Abs8 returns the absolute value of i (calculated without branching).
+func Abs8(i int8) int8 {
+	const bits = 8
+	u := uint64(i >> (bits - 1))
+	return (i ^ int8(u)) + int8(u&1)
+}
+
+// Abs16 returns the absolute value of i (calculated without branching).
+func Abs16(i int16) int16 {
+	const bits = 16
+	u := uint64(i >> (bits - 1))
+	return (i ^ int16(u)) + int16(u&1)
+}
+
+// Abs32 returns the absolute value of i (calculated without branching).
+func Abs32(i int32) int32 {
+	const bits = 32
+	u := uint64(i >> (bits - 1))
+	return (i ^ int32(u)) + int32(u&1)
+}
+
+// Abs64 returns the absolute value of i (calculated without branching).
+func Abs64(i int64) int64 {
+	const bits = 64
+	u := uint64(i >> (bits - 1))
+	return (i ^ int64(u)) + int64(u&1)
+}