fix: remove unnecessary fields from tools' inputSchema

[fpoli]

This PR cleans up the inputSchema generation of MCP tools, removing the unnecessary top-level fields mentioned in #847.

In more detail, the PR adds a schema_for_input wrapper around schema_for_type. The wrapper prepares the inputSchema of macro-generated tool descriptions, removing the top-level title and description fields (i.e. the type name and doc of T in Parameters<T>).

Motivation and Context

See #847. To sum up, I think the top-level title and description fields are unnecessary:

1. They are not useful. They describe a wrapper type (the T in Parameters<T>) that should not be leaked to the LLM. See these examples. What matters is the type and docs of the fields of T, which remain in the inputSchema and are not modified by this PR.
2. The fields are not required by the MCP specification (schema). They add noise that can reach the model and consume context tokens.

How Has This Been Tested?

By adding a test_list_tools_result.rs, which compares the tool description against a reference description in a JSON file.

(No) Breaking Changes

The top-level title and description disappear from the inputSchema. This is not a breaking change because the fields are not part of the MCP specification.

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

Fixes #847.

[jamadeo]

Makes sense to me