perf(core): avoid primitive fingerprint boxing

[TypeThe0ry]

What changed

• add exact-output boolean, char, and int overloads to DelimitedFingerprintBuilder.field
• keep the existing object/null, delimiter, raw, and entry-separator semantics unchanged
• add focused regression coverage for primitive text encoding and fallback behavior

Why

Hot render/HUD signature paths currently route primitive values through field(Object), which boxes them and materializes an intermediate string before appending. The primitive overloads append directly to the existing StringBuilder. The char overload is required so Java widening to int cannot change character output.

Validation

No Gradle, JMH, test, or server workload was run locally, per project policy. GitHub Build/Test is the functional gate. This PR stays draft and must not merge until the base-owned A/B lock fix (#60) lands and the protected fingerprint profile reports PASS_OPTIMIZED; a separate base-owned harness change will also enforce exact JMH output and allocation evidence.

[TypeThe0ry]

Trusted base-owned performance A/B evidence:

• Run: https://github.com/EllanServer/MahjongEngine/actions/runs/29475512830
• Base: 610535d49167b47f3808324a06fe17287f167f0c
• Candidate: 4d6f99899fe9edc6d48819172cecaf11afe1827d
• Profile: infra (default forks/warmups/measurements; 4 AB + 4 BA pairs)
• Decision: PASS_OPTIMIZED
• Time (ns/op, lower is better): paired median improvement 16.6572%; 95% bootstrap CI 14.7750%–17.7400%; 8/8 wins, 0 losses/ties.
• Allocation (B/op, lower is better): paired median improvement 7.31708% (352.000 → 328.000 B/op); 95% bootstrap CI 7.3170778%–7.3170793%; 8/8 wins, 0 losses/ties.
• A/A drift control passed.
• Evidence artifact: performance-ab-infra-610535d49167b47f3808324a06fe17287f167f0c-4d6f99899fe9edc6d48819172cecaf11afe1827d (ID 8366666457, SHA-256 994dbaf5e1e5ef2c1b78f2755f71d2b84d4f8e9a50d7f1383d52f208d3a2e90a).