Modularize cleartext specifications for the bitcoin app

[bigspider]

Move bip388/cleartext into standalone crate.
Move both the specs and the test vectors in a a folder containing toml files.

[Copilot]

Pull request overview

This PR extracts the BIP388 cleartext display/specification logic from the Bitcoin common crate into a new standalone apps/bitcoin/bip388 crate, and migrates the cleartext specification + test vectors into TOML files to be consumed by codegen and tests.

Changes:

• Introduces a new bip388 crate containing the BIP388 parsing/types plus cleartext encode/decode support and code generation via build.rs.
• Moves the cleartext specification and test vectors into src/cleartext/specs/*.toml and updates the codegen/test harness to consume them.
• Updates the Bitcoin common crate to depend on and re-export the new bip388 crate; updates CI and workspace configuration to include the new crate.

Reviewed changes

Copilot reviewed 11 out of 13 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
vanadium.code-workspace	Adds the new apps/bitcoin/bip388 folder to the workspace config.
apps/bitcoin/common/src/lib.rs	Switches from an internal bip388 module to re-exporting the external bip388 crate.
apps/bitcoin/common/src/bip388/cleartext/mod.rs	Removes the old in-crate cleartext implementation (moved to the new crate).
apps/bitcoin/common/Cargo.toml	Drops cleartext codegen build deps and adds a path dependency on ../bip388.
apps/bitcoin/bip388/Cargo.toml	Adds the new bip388 crate manifest, features, and build/dev dependencies.
apps/bitcoin/bip388/build.rs	Implements cleartext code generation from src/cleartext/specs/cleartext.toml.
apps/bitcoin/bip388/src/lib.rs	Defines the new crate root, wiring in cleartext/time and re-exporting cleartext API.
apps/bitcoin/bip388/src/time.rs	Adds time/date formatting + parsing helpers used by cleartext.
apps/bitcoin/bip388/src/cleartext/mod.rs	Adds the cleartext encode/decode + confusion score logic and TOML-driven test harness.
apps/bitcoin/bip388/src/cleartext/decode.rs	Updates decode module comment to reference the new spec path.
apps/bitcoin/bip388/src/cleartext/specs/cleartext.toml	Adds the TOML “single source of truth” cleartext spec consumed by codegen.
apps/bitcoin/bip388/src/cleartext/specs/test_vectors.toml	Adds shared TOML test vectors for encoder/decoder behavior.
.github/workflows/ci.yaml	Ensures native tests run in the new apps/bitcoin/bip388 directory.

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