Preserve exact type matches in union conversion

[iamramtin]

Description

Fixes union type conversion issue where Value.Parse() unnecessarily converts values to the first matching type in a union, even when the input already matches one of the union types exactly.

Problem

When using unions like Type.Union([Type.String(), Type.Number()]), numeric values were being converted to strings because the conversion logic would coerce to the first compatible type rather than preserving the original when it's already valid.

// Before (broken)
const schema = Type.Union([Type.String(), Type.Number()])
Value.Parse(schema, 42) // Returns "42" (string) instead of 42 (number)

// After (fixed)  
Value.Parse(schema, 42) // Returns 42 (number), which correctly preserves type

Fixes #1281

[sinclairzx81]

@iamramtin Hi, thanks for the PR

Hey sorry about the delay getting this PR looked at. I have been extraordinarily busy on other project work of late which has meant I have had to defer PR reviews, sorry about that.

This said, everything looks great here (and this is a nice fix to improve things for order independent unions!). Happy to merge this one in.

Will publish out later today and let you know once published on this thread.
Thanks again!

[sinclairzx81]

@iamramtin Hiya,

Updates published on 0.34.38.

Thanks again for the PR, and again, sorry for the delay.
All the best!
S

[iamramtin]

Hey @sinclairzx81, all good, thanks for merging this in. I appreciate the work you're doing here with typebox!