Calling setmaxstdio(u32::MAX) caused crashes due to integer overflow when casting to c_int. Values exceeding 2,147,483,647 wrapped to negative numbers, triggering undefined behavior in Windows CRT's _setmaxstdio.

Changes

• Input validation: Reject values > c_int::MAX with InvalidInput error before calling underlying C function
• Documentation: Clarified platform-dependent limits (typically 8,192 max) and error conditions
• Tests: Added coverage for u32::MAX and boundary conditions

Example

// Previously: crashed or undefined behavior
setmaxstdio(u32::MAX)?; 

// Now: returns Err with InvalidInput
assert!(setmaxstdio(u32::MAX).is_err());
assert!(setmaxstdio(c_int::MAX as u32 + 1).is_err());

// Valid calls unchanged
setmaxstdio(2048)?; // OK

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• Fixes Final review before 1.0 #27

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