fix: Avoid collisions in CacheKeyBuilder.

[gianm]

This patch adds a length prefix before each item when building cache keys. This avoids ambiguity in situations where a cache key itself contains a valid type code.

[FrankChen021]

Severity	Findings
P0	0
P1	1
P2	0
P3	0
Total	1

Reviewed 6 of 6 changed files.

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This is an automated review by Codex GPT-5.6-Luna(max)

[FrankChen021]

[P1] Version the new cache-key format

This changes the serialized bytes for every CacheKeyBuilder key, but the output still uses only the caller-supplied id and does not distinguish the new format from the old one. During a rolling upgrade, shared caches such as Memcached can retain old entries; the two formats are not disjoint, so a new key can be an old-format key for a different public builder sequence (for example, old appendByte(0).appendByte(0).appendByteArray(new byte[]{v}) produces the same bytes as new appendByte(v) for the same id). That can turn a miss into a false hit and return another query's result. Add a format/version discriminator or explicitly isolate/invalidate old entries, and add a mixed-version collision regression test.