perf(hash): add inline FNV-1a hash functions to internal/hash package

Zero-allocation alternative to hash/fnv.New64a(). Computes FNV-1a
inline without heap-allocating a hash.Hash64 object per call.

internal/hash/hash.go

@@ -0,0 +1,19 @@
+package hash
+
+func FNV64a(key string) uint64 {
+	var h uint64 = 14695981039346656037
+	for i := 0; i < len(key); i++ {
+		h ^= uint64(key[i])
+		h *= 1099511628211
+	}
+	return h
+}
+
+func FNV64aBytes(key []byte) uint64 {
+	var h uint64 = 14695981039346656037
+	for i := 0; i < len(key); i++ {
+		h ^= uint64(key[i])
+		h *= 1099511628211
+	}
+	return h
+}