feat: improve schema simplification with composition support and cycle detection

[VarunAthreya]

Summary

• Refactor schema simplification to handle allOf, anyOf, and oneOf composition keywords properly
• Add cycle detection for recursive/circular schema types to prevent infinite expansion
• Implement node counting with a configurable limit (10,000) to bound schema output size
• Improve type inference with fillImpliedTypes to infer missing type declarations
• Add comprehensive test coverage for complex schema scenarios
• Fixes: deck file openapi2mcp command not handling $ref and allOf / anyOf correctly deck#2200

Changes

Code Changes

• openapi2mcp.go:
  • Replace simple simplifySchema() function with schemaSimplifier struct for stateful schema traversal
  • Track in-progress references to detect cycles and log them at debug level
  • Implement maxSchemaNodes limit to prevent exponential expansion in dense schema graphs
  • Add inlineSchema() as the public API with logging for truncated schemas
  • Improve handling of composition keywords per OpenAPI spec semantics

Tests

• Add 4 new test fixtures covering complex schema scenarios:
  • 10-schema-allof.yaml: Test allOf member merging
  • 11-schema-oneof-anyof.yaml: Test anyOf/oneOf branch preservation
  • 12-schema-circular.yaml: Test recursive/circular schema truncation
  • 13-schema-params.yaml: Test parameters with complex composed schemas
• Refactor common test pattern into assertFixtureConversions helper

Documentation

• Expand README.md with detailed explanation of:
  • Composition keyword handling (allOf, anyOf, oneOf)
  • Recursive schema truncation and node limits
  • Type inference behavior for simplified schemas

[codecov-commenter]

Codecov Report

❌ Patch coverage is 94.88372% with 11 lines in your changes missing coverage. Please review.
✅ Project coverage is 60.65%. Comparing base (afc605e) to head (cabd0c2).

Files with missing lines	Patch %	Lines
openapi2mcp/openapi2mcp.go	94.88%	6 Missing and 5 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #303      +/-   ##
==========================================
+ Coverage   58.82%   60.65%   +1.82%     
==========================================
  Files          36       36              
  Lines        3869     4059     +190     
==========================================
+ Hits         2276     2462     +186     
- Misses       1380     1382       +2     
- Partials      213      215       +2     

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