Code hygiene: unused import, `raise exc` drops traceback context

[AndresL230]

Summary

Two trivial fixes:

1. Unused import

ruff check reports F401 unused-import for MAX_BUCKETS in recost/_transport.py:23.

2. Traceback rebound

recost/_interceptor.py:148-156, 219-228, 266-275, 342-350 re-raise via raise exc rather than bare raise, rebinding the traceback. End users debugging SDK-wrapped errors see the SDK wrapper at the top of the stack, not their own call site.

Fix

• Remove the unused import.
• Replace every raise exc with bare raise.

Files

• recost/_transport.py
• recost/_interceptor.py

Priority

P2 — pure code hygiene; the traceback issue affects end-user debugging experience.