Bzlib macros

[folkertdev]

clean up some of the macros and remove bounds checks that are not needed (because the slices have the length that is being checked for).

[codecov]

Codecov Report

Attention: Patch coverage is 80.00000% with 3 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
libbz2-rs-sys/src/bzlib.rs	80.00%	3 Missing ⚠️

Files with missing lines	Coverage Δ
libbz2-rs-sys/src/bzlib.rs	92.62% <80.00%> (ø)