Add some function inlining

[kylebarron]

• I agree to follow the project's code of conduct.
• I added an entry to CHANGES.md if knowledge of this change could be valuable to users.
• I ran cargo fmt

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It turns out function inlining can have a surprisingly big effect on the benchmark:

Benchmarking parse small to geo: Collecting 100 samples in estimated 5.0001 s (42M itera
parse small to geo      time:   [125.30 ns 125.89 ns 126.34 ns]
                        change: [-12.615% -11.585% -10.646%] (p = 0.00 < 0.05)
                        Performance has improved.

Benchmarking parse big to geo: Collecting 100 samples in estimated 5.2794 s (40k iterati
parse big to geo        time:   [130.44 µs 131.96 µs 133.69 µs]
                        change: [-16.388% -15.530% -14.647%] (p = 0.00 < 0.05)
                        Performance has improved.
Found 18 outliers among 100 measurements (18.00%)
  16 (16.00%) low mild
  2 (2.00%) high severe

That brings the parse to 2.8x faster than shapely.wkb.loads (see #37)