fix: align URI template matching with RFC 6570 operators

[leehack]

Summary

• Fix URI template matching to use operator-correct separators for multi-variable RFC 6570 expressions (? then &, # then ,, etc.) so valid URIs are matched correctly.
• Escape variable names while building regex patterns in match() to avoid regex edge cases.
• Add regression tests for the issue case (entity://list{?status,assignee}) and a server resources/read flow that now resolves this template URI.

Fixes #68

Testing

• dart test test/shared/uri_template_test.dart
• dart test test/server/mcp_test.dart
• dart analyze
• dart test

[codecov]

Codecov Report

❌ Patch coverage is 44.44444% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 78.50%. Comparing base (6f8795b) to head (66e54de).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
lib/src/shared/uri_template.dart	44.44%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #69      +/-   ##
==========================================
+ Coverage   78.47%   78.50%   +0.03%     
==========================================
  Files          40       40              
  Lines        5091     5095       +4     
==========================================
+ Hits         3995     4000       +5     
+ Misses       1096     1095       -1     

Flag	Coverage Δ
unittests	78.50% <44.44%> (+0.03%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.