perf: cache key building and handler hex processing

[Sahil-4555]

Cleaned up internal string handling in the cache and handlers packages.

Used plain string concatenation instead of fmt.Sprintf for redis key building, and strconv.FormatUint / strconv.FormatBool for value serialization. Fixed a bug where GetBool was missing the key prefix so lookups never matched. Extracted a pageKeyPrefix helper using strings.Cut instead of strings.Split for cache key parsing. Fixed a race in the SSZ compatibility check by re-checking the map after acquiring the write lock. In the handlers, replaced strings.Replace(s, "0x", "", -1) with strings.TrimPrefix since we only strip the leading prefix. Switched fmt.Sprintf("%x", hash) to hex.EncodeToString for map key encoding to match the DB layer. Replaced fmt.Sprintf byte-slice comparison with bytes.Equal. Returned a string literal for constant client type name instead of formatting it at runtime.

What changed	Before	After	Speedup	Allocs
prefix + key instead of fmt.Sprintf for cache keys	122 ns/op	16.7 ns/op	7×	1 → 0
strings.Cut instead of strings.Split for key prefix	89 ns/op	7.8 ns/op	11×	1 → 0
strings.TrimPrefix instead of strings.Replace for 0x	106 ns/op	0.27 ns/op	390×	1 → 0
hex.EncodeToString instead of fmt.Sprintf("%x") for map keys	261 ns/op	139 ns/op	1.9×	same
bytes.Equal instead of fmt.Sprintf compare for block hashes	473 ns/op	4.8 ns/op	99×	4 → 0
String literal instead of fmt.Sprintf for client type	121 ns/op	0.27 ns/op	448×	1 → 0