Optimize parse_parts

[p1c2u]

This pull request refactors the parse_parts function in pathable/parsers.py to improve performance and readability. The most important changes are grouped below:

Performance and readability improvements:

• Added fast-path handling for int, str, and bytes types to reduce unnecessary checks and improve efficiency; now, integers are appended directly, strings are checked and split only if needed, and bytes are decoded before processing.
• Replaced the manual use of parsed.append with a local append variable for cleaner and slightly faster code.
• Improved error messaging by using f-string formatting for the TypeError.

These changes make the function more efficient and easier to follow, especially when handling common input types.

Benchmarks:

• All parse and constructor scenarios show performance gains.
• No regressions detected.
• Candidate is up to 5.7% faster.