fix: return all codes in toCodes() for custom locale paths

[axu6705]

Changes

• Modified the toCodes function implementation from map to flatMap to support expanding all language codes
• Now returns all language codes (codes) instead of just the first one (codes[0])

Testing

N/A

Docs

N/A

[codspeed-hq]

CodSpeed Performance Report

Merging #13438 will not alter performance

_{Comparing axu6705:fix/custom-locale-paths (e4170da) with main (1eab0b2)}

Summary

✅ 6 untouched benchmarks

[ematipico]

@axu6705 please test your changes, because it's breaking the CI.

So, what you need to do:

• provide a changeset that highlights what bug was fixed
• add a new test