improve JPEG encode_block perf by about 25% with faster integer encoding

[mcroomp]

I license past and future contributions under the dual MIT/Apache-2.0 license,
allowing licensees to choose either at their option.

Also add benches for tracking performance of JPEG block encoding.

pre:
test codecs::jpeg::encoder::tests::bench_encode_block ... bench: 548 ns/iter (+/- 131) = 135 MB/s
post:
test codecs::jpeg::encoder::tests::bench_encode_block ... bench: 410 ns/iter (+/- 140) = 180 MB/s

[mcroomp]

Looks like NonZeroU32::unsigned_abs was stabilized in 1.64... let's see if there's a workaround

[197g]

We can also bump MSRV for a perf win, it's not a set-in-stone restriction. Bump here and as indicated in the comment to do it with the PR:

https://github.com/image-rs/image/blob/master/Cargo.toml#L7-L8

[Shnatsel]

I see MSRV has been bumped to 1.67 since, which is higher than this PR's requirement of 1.64.

I understand there is nothing blocking this, and it can be merged?

The change is simple, covered by tests, and the performance gains are tantalizing.

[fintelia]

Will look into reviving this PR once 0.25.0 is out

[mcroomp]

Rebased since this change had sat there for a while

[mcroomp]

There's still a CI test_toolchain with 1.63 that needs to be upgraded before this can be integrated

[fintelia]

Thanks for this PR!

I think it is kind of doing a lot and would be better split into a bunch of PRs. Perhaps:

1. Adding benchmarks to give a baseline performance number and justify subsequent PRs
2. Optimizations to BitWriter
3. New version of write_block
4. New version of encode_coefficient

[fintelia]

I don't think we should keep around an old implementation simply to benchmark against

[Shnatsel]

This is superseded by #2636 which replaced the in-tree JPEG encoder with the jpeg-encoder crate.