[ikripaka]

• This PR suggests a bug fix and I've added the necessary tests.
• This PR introduces a new feature and I've discussed the update in an Issue or with the team.
• This PR is just a minor change like a typo fix.

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Migrate simplicity-std to the 0.2.0 simplex version.
Format contracts with the simplex formatter, add CI check.
According to this issue: BlockstreamResearch/rust-simplicity#389, I added patch tests from

I used this pr BlockstreamResearch/rust-simplicity#402; it all works with our contracts.
A new one: BlockstreamResearch/rust-simplicity#403 doesn't compile.
Later, we should remove it.

Why do we need to sign with NativeSignature::Ecdsa in simplicity-std/tests/stdlib/common/core.rs?
The signing API changed in simplex, so it explicitly mentions what you sign instead of implicitly.
Before the refactor, we fell back to the last else case, which signed inputs.

[LesterEvSe]

Also, we need to add an entry to CHANGELOG.md stating that we:
- Bumped Simplex to 0.2.0..

Additionally, it is best to check whether the current version works with older versions and update README.md accordingly. To be precise, this line:

> [!NOTE]
> The library works with Simplex versions 0.x.x or higher.

[ikripaka]

effef25 - apply lint suggestions
24baada - update Changelog and Readme

[LesterEvSe]

Note on the supported Simplex range, for future reference.

Users compile std's .simf sources with the SimplicityHL compiler that their Simplex bundles, so the lower bound mostly follows HL. Std doesn't use anything added after HL 0.6.0 (modules), which Simplex 0.0.7 bundles.

Developing std is stricter: the Rust test harness uses fuzz testing (added in Simplex 0.1.0) and APIs that changed in 0.2.0, so running the tests needs Simplex 0.2.0 or later. The user-side bound will move once std uses something newer, e.g. a simc version directive or enum. The Simplex.toml change in this PR only updates our commented-out template to the 0.2.0 one, so it has no effect on users.

nit (for later): we could move this into a dev doc (e.g. docs/dev/) to track it more explicitly as HL and Simplex evolve

[LesterEvSe]

ACK 3508a8c; tested locally with simplex test --test-threads 7 --no-fail-fast -- --release

[ikripaka]

Rebased onto the new dev branch: b04a022.
Don't change any files.

[Hrom131]

LGTM!