fix: speed up int_to_bluetooth_address C implementation

[akx]

Similar to bdraco/ulid-transform#43.

I think the previous implementation also had a memory leak, unless Cython somehow implicitly took care of free()ing the mallocated bdaddr.

---

Seems to be a 12.5% speed improvement on test_parse_int_to_bluetooth_address_uncached on my machine.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (595c65a) to head (4d8f9a8).
Report is 14 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main       #52   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            6         6           
  Lines          230       230           
  Branches        34        34           
=========================================
  Hits           230       230           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.