feat: enable no_std compilation and check it in CI

[JoseSK999]

Description

This PR adds two new dependencies that are needed for no_std support: hashbrown (HashMap alternative) and bitcoin_io (io trait and type replacements).

The AccumulatorHash trait bounds depend on whether we use std or no_std now.

Note

This seems to work but perhaps we should add a feature powerset CI check to ensure all 4 combinations work fine for clippy and testing.

The prelude list is from floresta-common, I think I can trim a couple of these imports.

[Davidson-Souza]

Just to make sure: you can't disable a dependency if a feature is on, right? You can only enable them. Because now we have at least one non rust-bitcoin dependency that's not feature-gated. I guess it's ok, since hashbrown is super small and is the basis for std's hashmap implementation

[JoseSK999]

Yes, sort of ugly. Otherwise we would have to create a no-std or hashbrown feature required for no-std.

But as you say, std::collections::HashMap is wrapping the hashbrown one: https://doc.rust-lang.org/src/std/collections/hash/map.rs.html

[JoseSK999]

Pushed 21ae740

• Cleanup the prelude mod, now it's mostly exporting alloc items to mirror the std prelude, io and HashMap/HashSet
• Imported some items

And very important:

• Test and check rustreexo without the std feature (this catched doctest issues and a panic in tests)

[luisschwab]

@JoseSK999 you could also add a test-no-std recipe to the justfile and have CI run the recipe, so we can avoid duplication and have the justfile as the single source of truth for testing.

[JoseSK999]

@JoseSK999 you could also add a test-no-std recipe to the justfile and have CI run the recipe, so we can avoid duplication and have the justfile as the single source of truth for testing.

I had extended the just test recipe to test no default features (i.e., no-std), I think better than a separate just test-no-std. But CI is not using just test. Should I make the recipe be

test:
    cargo +nightly test --no-default-features
    cargo +nightly test --all-features
    cargo +stable test --no-default-features
    cargo +stable test --all-features

and use it in CI? (not sure)

[luisschwab]

Oh, I thought I had changed CI to use the justfile's recipes. I think that is a better approach (I do it on my own repos). Thoughts @Davidson-Souza

[JoseSK999]

CI here uses just check and just test-msrv, but not just test

[luisschwab]

I guess that just test and just test-msrv should be extended to check for no-std and have CI use those instead.

[JoseSK999]

So I have made just test delegate to just test-stable and just test-nightly. In CI we now call these two 👺

just test-{stable/nightly/msrv} and just check are all now running with --no-default-features too