feat: no_std

[JonasKruckenberg]

As promised: This PR adds no_std support to zlib-rs, by adding two new feature flags std and alloc that hide related functionality behind them (enabled by default).

I also had to disable the auto-detection of features which is not yet exposed through feature flags.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 95.23810% with 12 lines in your changes are missing coverage. Please review.

Project coverage is 90.60%. Comparing base (751c803) to head (91ddd87).

:exclamation: Current head 91ddd87 differs from pull request most recent head 81c3a2e. Consider uploading reports for the commit 81c3a2e to get more accurate results

Files	Patch %	Lines
zlib-rs/src/read_buf.rs	55.55%	4 Missing :warning:
zlib-rs/src/deflate/algorithm/stored.rs	66.66%	2 Missing :warning:
zlib-rs/src/inflate.rs	94.87%	2 Missing :warning:
zlib-rs/src/adler32/avx2.rs	0.00%	1 Missing :warning:
zlib-rs/src/allocate.rs	98.68%	1 Missing :warning:
zlib-rs/src/deflate.rs	98.41%	1 Missing :warning:
zlib-rs/src/inflate/bitreader.rs	75.00%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #97 +/- ## ========================================== + Coverage 87.64% 90.60% +2.95% ========================================== Files 34 36 +2 Lines 8790 9181 +391 ========================================== + Hits 7704 8318 +614 + Misses 1086 863 -223 ```

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[folkertdev]

I made it so that cargo check at least works for --target thumbv7em-none-eabihf now with the zlib-rs crate itself. If you're OK with some API breakage in the future that should provide everything you need to play around with this I think.

But maybe not, let me know. Also

• can you rebase this on main. I think I messed something up in git and I cannot force push to this branch
• do you have thoughts on how to test this in CI? would a working (but with warnings) cargo check --target thumb* provide enough stability?

[folkertdev]

turns out I can force push. I think this is ready to merge, but would like to try it out on actual embedded hardware just to make sure there are no unexpected issues. I'll try to do that tomorrow