Reject non-finite JSON numbers

[leehack]

Summary

• add shared finite JSON-number validation helpers
• reject NaN and infinity for progress values, annotation/model priorities, and sampling temperature on parse/serialization
• cover stable 2025-11-25 and 2026-07-28 RC numeric schema regressions

Validation

• dart format .
• dart test test/types_edge_cases_test.dart
• dart test test/types/sampling_test.dart
• dart test test/mcp_2025_11_25_test.dart
• dart test test/mcp_2026_07_28_test.dart
• dart analyze
• dart test
• dart run mcp_dart_cli:mcp_dart conformance --suite all --json

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.13%. Comparing base (e3cecc7) to head (b1134cd).

Additional details and impacted files

@@                           Coverage Diff                           @@
##           spec/elicitation-url-uri-validation     #220      +/-   ##
=======================================================================
+ Coverage                                88.10%   88.13%   +0.03%     
=======================================================================
  Files                                       47       47              
  Lines                                     9161     9179      +18     
=======================================================================
+ Hits                                      8071     8090      +19     
+ Misses                                    1090     1089       -1     

Flag	Coverage Δ
unittests	88.13% <100.00%> (+0.03%)	⬆️

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[leehack]

Closing this draft micro PR because the RC spec work has been consolidated into a smaller reviewable stack. This change is preserved in #270 (JSON-RPC metadata hardening); the consolidated tip is tree-identical to the previous micro-stack tip.