Add Zstd support as optional and compile-time low ratio report

[kkent030315]

Zstd (ZStandard) is a fast real-time compression algorithm.

I've added Zstd support in compression/decompression as optional. Users can select which one to use by specifying feature flags: zstd and deflate.

# Cargo.toml
[dependencies]
include-flate = { version = "...", default-features = false, features = ["zstd"] }
# or
include-flate = { version = "...", default-features = false, features = ["deflate"] } # this is same as default.

In summary, while DEFLATE is a venerable and widely adopted algorithm, Zstd provides significant advantages in speed and compression ratio, would make it a strong choice for crates or binaries that can support it.

Testing this PR

Since I've modified Cargo.toml to not use unnecessary dependency, multiple vectors of tests needed:

cargo test --all

cargo test --no-default-features --features deflate

cargo test --no-default-features --features zstd

[SOF3]

in that case, consider using the CI pipeline for different features too?

[kkent030315]

Well, It's done and awaiting for your @SOF3 review.

Changelog

• Added: Zstd support for compression.
  • I've added custom encoders, FlateEncoder and FlateDecoder, for each of the current and future compression methods that the encoders/decoders need to wrap. That means, it is just to write an wrapper for both FlateEncoder and FlateDecoder and adding some values into some enums are enough to add custom compression method in further. And of course, I've improved tests, so additional compression methods could be tested more precisely.
• Added: include-flate-compress in compress folder in the root directory of this repository, for commonality.
• Added: FlateArgs for extendable/descriptive TokenStream input.
• Improved: Entire tests are improved for additional checks regarding compression.
• Improved: test_util.rs has been reworked for reliable code.
• Improved: Better error message in decompression failure in include_flate::decode function.

The compression features are selectable for each flate! macros, or DEFLATE by default:

flate!(pub static DATA: [u8] from "assets/009f.dat"); // default, DEFLATE
flate!(pub static DATA: [u8] from "assets/009f.dat" with zstd); // Use Zstd for this file spcifically
flate!(pub static DATA: [u8] from "assets/009f.dat" with deflate); // Explicitly use DEFLATE.

[kkent030315]

in that case, consider using the CI pipeline for different features too?

As of now, I've pivoted to not use Cargo feature, CI changes shouldn't required. (Reverted in 957c2bf)

[kkent030315]

I’ve also added compile-time warning for less compression binaries, so they have a visibility for compression ration for each binaries and can consider another compression method if it is not they're looking for.

Also for the users want to ignore this warning, I've added no-compression-warnings feature, which is disabled by default.

[kkent030315]

@SOF3 For the compression ratio warning, we should have discussion about:

1. Should it be disabled by default? I think so.
2. What do you think the best threshold is? Currently, it is set to 10%.

[SOF3]

10% sounds right to me. Users should be aware that include_flate does not just increase executable size — it also increases the runtime memory by doubling the required storage and hence only reasonable to use when compression ratio is sufficiently high.

Might be useful to provide a deflate_if in a future (separate) feature too.

[kkent030315]

Okay, l will work on fixing CI.

[kkent030315]

It should be ok for now. please run the CI.

[SOF3]

Thanks! Will do a release later.