fix: improve tool() parameter parsing to handle undefined values

[grimmerk]

Rewrites parameter parsing to find callback first, then parse args sequentially by type. Handles edge cases where optional params (description, paramsSchema, annotations) may be undefined.

Fixes cases like:

• tool(name, undefined, schema, undefined, callback)
• tool(name, description, undefined, annotations, callback)
• tool(name, undefined, schema, callback)

Motivation and Context

When tool() is called with undefined in optional parameter positions, the original shift-based parsing logic fails because:

• typeof undefined !== "object" causes undefined values to be skipped incorrectly
• Sequential shift() operations lose track of parameter positions

This happens in real-world scenarios when:

• Parameters come from optional config objects (config.annotations may be undefined)
• TypeScript strict mode is disabled in consuming projects
• Dynamic tool registration uses conditional parameters

The fix improves runtime robustness without changing the public API, maintaining backward compatibility while handling edge cases more gracefully.

How Has This Been Tested?

• ✅ All 79 unit tests pass (77 existing + 2 new)
• ✅ Added test: tool(name, undefined, schema, callback) - description undefined
• ✅ Added test: tool(name, desc, undefined, annotations, callback) - paramsSchema undefined
• ✅ Added test: tool(name, desc, schema, undefined, callback) - annotations undefined
• ✅ Each test verifies both tool registration and callback execution work correctly
• ✅ Build passes for both ESM and CJS outputs

Breaking Changes

None. This is a non-breaking internal fix:

• Public API signatures unchanged
• Existing valid usage patterns continue to work
• Only improves handling of edge cases that previously failed

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed

Additional context

Implementation approach:

1. Find callback first (search backwards for last function in args)
2. Extract all parameters before callback
3. Parse sequentially with explicit undefined handling:
   • Check if arg matches expected type → assign & advance
   • Check if arg is undefined → skip & advance
   • Otherwise → don't advance (might be next param type)

This callback-first approach is more robust than the original shift-based logic because it establishes a fixed reference point (the callback) before parsing optional parameters.

Error handling:
Added validation to throw clear error if no callback function is found in arguments.