Fixes incorrect casting into int for numbers in string format

[kafkasl]

Fixes #316

When a parameter in fastMCP is a number, but the type of the tool is string, it is regardless casted into int, and thus the tool fails. This issue was solved in the original FastMCP repo but apparently it was lost. I just added the code back as suggested together with its test.

Original fix

• PrefectHQ/fastmcp@07fc104

Current Issue report:

• Input should be a valid string [type=string_type, input_value=123, input_type=int] #316

Motivation and Context

Fixes tool input numbers being cast into int when they are specified as str.

How Has This Been Tested?

I added back the original test. It matches the errors I'm seeing when using FastMCP 1.5.0 in my project.

Breaking Changes

No

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

[dsp-ant]

Thank you! The fix seems to have gotten lost in translation to the official SDK.