feat(string): add Clone — detach string from backing memory

Adds core.Clone, the canonical wrapper for strings.Clone. Used when
a string aliases a reusable scratch buffer (e.g. via core.AsString
over a re-sliceable byte buffer) and the resulting string must
outlive the buffer's next reuse — map keys, struct fields, channel
sends across goroutines.

Driven by the gguf metadata loop in go-inference: the parser reads
keys into a reusable byte buffer and only stores the ~7 keys
ReadGGUFInfo queries. Without Clone, mapping a zero-copy view into
a map[string]any would risk later mutation aliasing the key.

Co-Authored-By: Virgil <virgil@lethean.io>

Author: Snider

string.go

@@ -40,6 +40,16 @@ func TrimSuffix(s, suffix string) string {
 	return strings.TrimSuffix(s, suffix)
 }
 
+// Clone returns a fresh copy of s, detached from its backing memory.
+// Use this when s aliases a reusable buffer (e.g. via core.AsString
+// over a scratch slice) and the result must outlive the buffer's
+// next reuse — map keys, struct fields, channel sends.
+//
+//	key := core.Clone(core.AsString(scratch))  // map[key] = ... is safe
+func Clone(s string) string {
+	return strings.Clone(s)
+}
+
 // Contains returns true if s contains substr.
 //
 //	core.Contains("hello world", "world")  // true