optimize: limit allowlist cache growth

[LegendPei]

• I have read the CONTRIBUTING.md guidelines.
• I have registered the PR changes.

Ⅰ. Describe what this PR did

Limit the growth of the JSON deserialization allowlist cache.

This PR updates JsonAllowlistManager to:

• reject overlong class names before allowlist checking
• cache only allowed class names
• avoid caching rejected class names
• cap the allowlist cache size to prevent unbounded memory growth

It also adds unit tests covering rejected class names, overlong class names, cache hits, and cache size limits.

Ⅱ. Does this pull request fix one issue?

Ⅲ. Why don't you add test cases (unit test/integration test)?

Added unit tests in JsonAllowlistManagerTest.

Ⅳ. Describe how to verify it

Ⅴ. Special notes for reviews

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 73.01%. Comparing base (9c235df) to head (8e8df76).

Additional details and impacted files

@@             Coverage Diff              @@
##                2.x    #8120      +/-   ##
============================================
+ Coverage     72.80%   73.01%   +0.21%     
  Complexity      883      883              
============================================
  Files          1327     1327              
  Lines         50719    50734      +15     
  Branches       6049     6052       +3     
============================================
+ Hits          36924    37043     +119     
+ Misses        10802    10691     -111     
- Partials       2993     3000       +7     

Files with missing lines	Coverage Δ
...apache/seata/common/json/JsonAllowlistManager.java	95.23% <100.00%> (+0.46%)	⬆️

... and 15 files with indirect coverage changes

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