[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/pack.go

@@ -0,0 +1,85 @@
+package bitutil
+
+// PackInt8s will pack two signed 8bit integers into an unsigned 16bit integer.
+func PackInt8s(i1, i2 int8) uint16 {
+	const bits = 8
+	const mask = (1 << bits) - 1
+	return uint16(i1)<<bits | uint16(i2)&mask
+}
+
+// UnpackInt8s will unpack two signed 8bit integers from an unsigned 16bit integer.
+func UnpackInt8s(i uint16) (int8, int8) {
+	const bits = 8
+	const mask = (1 << bits) - 1
+	return int8(i >> bits), int8(i & mask)
+}
+
+// PackInt16s will pack two signed 16bit integers into an unsigned 32bit integer.
+func PackInt16s(i1, i2 int16) uint32 {
+	const bits = 16
+	const mask = (1 << bits) - 1
+	return uint32(i1)<<bits | uint32(i2)&mask
+}
+
+// UnpackInt16s will unpack two signed 16bit integers from an unsigned 32bit integer.
+func UnpackInt16s(i uint32) (int16, int16) {
+	const bits = 16
+	const mask = (1 << bits) - 1
+	return int16(i >> bits), int16(i & mask)
+}
+
+// PackInt32s will pack two signed 32bit integers into an unsigned 64bit integer.
+func PackInt32s(i1, i2 int32) uint64 {
+	const bits = 32
+	const mask = (1 << bits) - 1
+	return uint64(i1)<<bits | uint64(i2)&mask
+}
+
+// UnpackInt32s will unpack two signed 32bit integers from an unsigned 64bit integer.
+func UnpackInt32s(i uint64) (int32, int32) {
+	const bits = 32
+	const mask = (1 << bits) - 1
+	return int32(i >> bits), int32(i & mask)
+}
+
+// PackUint8s will pack two unsigned 8bit integers into an unsigned 16bit integer.
+func PackUint8s(u1, u2 uint8) uint16 {
+	const bits = 8
+	const mask = (1 << bits) - 1
+	return uint16(u1)<<bits | uint16(u2)&mask
+}
+
+// UnpackUint8s will unpack two unsigned 8bit integers from an unsigned 16bit integer.
+func UnpackUint8s(u uint16) (uint8, uint8) {
+	const bits = 8
+	const mask = (1 << bits) - 1
+	return uint8(u >> bits), uint8(u & mask)
+}
+
+// PackUint16s will pack two unsigned 16bit integers into an unsigned 32bit integer.
+func PackUint16s(u1, u2 uint16) uint32 {
+	const bits = 16
+	const mask = (1 << bits) - 1
+	return uint32(u1)<<bits | uint32(u2)&mask
+}
+
+// UnpackUint16s will unpack two unsigned 16bit integers from an unsigned 32bit integer.
+func UnpackUint16s(u uint32) (uint16, uint16) {
+	const bits = 16
+	const mask = (1 << bits) - 1
+	return uint16(u >> bits), uint16(u & mask)
+}
+
+// PackUint32s will pack two unsigned 32bit integers into an unsigned 64bit integer.
+func PackUint32s(u1, u2 uint32) uint64 {
+	const bits = 32
+	const mask = (1 << bits) - 1
+	return uint64(u1)<<bits | uint64(u2)&mask
+}
+
+// UnpackUint32s will unpack two unsigned 32bit integers from an unsigned 64bit integer.
+func UnpackUint32s(u uint64) (uint32, uint32) {
+	const bits = 32
+	const mask = (1 << bits) - 1
+	return uint32(u >> bits), uint32(u & mask)
+}