[chore] update dependencies (#4386)

- codeberg.org/gruf/go-bytesize v1.0.3 -> v1.0.4
- codeberg.org/gruf/go-kv/v2 v2.0.6 -> v2.0.7
- codeberg.org/gruf/go-mutexes v1.5.2 -> v1.5.3
- codeberg.org/gruf/go-structr v0.9.7 -> v0.9.8
- codeberg.org/gruf/go-ffmpreg v0.6.8 -> v0.6.9
- github.com/tomnomnom/linkheader HEAD@2018 -> HEAD@2025

all of the above codeberg.org/gruf updates are in preparation for Go1.25, except for bytesize, and also ffmpreg which is a rebuild with the latest version of ffmpeg (v5.1.7)

Reviewed-on: https://codeberg.org/superseriousbusiness/gotosocial/pulls/4386
Co-authored-by: kim <grufwub@gmail.com>
Co-committed-by: kim <grufwub@gmail.com>

vendor/codeberg.org/gruf/go-mangler/v2/struct.go

@@ -0,0 +1,75 @@
+package mangler
+
+import (
+	"unsafe"
+
+	"codeberg.org/gruf/go-xunsafe"
+)
+
+// field stores the minimum necessary
+// data for iterating and mangling
+// each field in a given struct.
+type field struct {
+	mangle Mangler
+	offset uintptr
+}
+
+// iterStructType returns a Mangler capable of iterating
+// and mangling the given struct type currently in TypeIter{}.
+// note this will fetch sub-Manglers for each struct field.
+func iterStructType(t xunsafe.TypeIter) Mangler {
+
+	// Number of struct fields.
+	n := t.Type.NumField()
+
+	// Gather mangler functions.
+	fields := make([]field, n)
+	for i := 0; i < n; i++ {
+
+		// Get struct field at index.
+		sfield := t.Type.Field(i)
+		rtype := sfield.Type
+
+		// Get nested field TypeIter with appropriate flags.
+		flags := xunsafe.ReflectStructFieldFlags(t.Flag, rtype)
+		ft := t.Child(sfield.Type, flags)
+
+		// Get field mangler.
+		fn := loadOrGet(ft)
+		if fn == nil {
+			return nil
+		}
+
+		// Set field info.
+		fields[i] = field{
+			mangle: fn,
+			offset: sfield.Offset,
+		}
+	}
+
+	// Handle no. fields.
+	switch len(fields) {
+	case 0:
+		return empty_mangler
+	case 1:
+		return fields[0].mangle
+	default:
+		return func(buf []byte, ptr unsafe.Pointer) []byte {
+			for i := range fields {
+				// Get struct field ptr via offset.
+				fptr := add(ptr, fields[i].offset)
+
+				// Mangle the struct field data.
+				buf = fields[i].mangle(buf, fptr)
+				buf = append(buf, ',')
+			}
+
+			if len(fields) > 0 {
+				// Drop final comma.
+				buf = buf[:len(buf)-1]
+			}
+
+			return buf
+		}
+	}
+}