Restrict elicitation content numbers to integers

[leehack]

Summary

• align ElicitResult.content numeric values with the current stable and draft schemas by allowing only integers
• normalize whole-number JSON numeric values to ints while rejecting fractional values
• update stable/draft regression coverage and the changelog note

Validation

• dart test test/elicitation_test.dart
• dart test test/mcp_2025_11_25_test.dart test/mcp_2026_07_28_test.dart
• dart analyze
• git diff --check
• dart test

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.62%. Comparing base (83814a7) to head (13d9fc9).

Additional details and impacted files

@@                         Coverage Diff                         @@
##           spec/integer-wire-field-validation     #260   +/-   ##
===================================================================
  Coverage                               88.61%   88.62%           
===================================================================
  Files                                      47       47           
  Lines                                    9472     9480    +8     
===================================================================
+ Hits                                     8394     8402    +8     
  Misses                                   1078     1078           

Flag	Coverage Δ
unittests	88.62% <100.00%> (+<0.01%)	⬆️

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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 #271 (type/schema validation); the consolidated tip is tree-identical to the previous micro-stack tip.