chore(rust-cktap): release v0.4.0

[bitcoindevkit-release-plz]

🤖 New release

• rust-cktap: 0.3.0 -> 0.4.0 (⚠ API breaking changes)

⚠ rust-cktap breaking changes

--- failure enum_variant_added: enum variant added on exhaustive enum ---

Description:
A publicly-visible enum without #[non_exhaustive] has a new variant.
        ref: https://doc.rust-lang.org/cargo/reference/semver.html#enum-variant-new
       impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.50.0/src/lints/enum_variant_added.ron

Failed in:
  variant CkTapError:UnknownErrorCode in /tmp/.tmpjzJz71/rust-cktap/lib/src/error.rs:19
  variant CkTapError:UnknownErrorCode in /tmp/.tmpjzJz71/rust-cktap/lib/src/error.rs:19

--- failure enum_variant_missing: pub enum variant removed or renamed ---

Description:
A publicly-visible enum has at least one variant that is no longer available under its prior name. It may have been renamed or removed entirely.
        ref: https://doc.rust-lang.org/cargo/reference/semver.html#item-remove
       impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.50.0/src/lints/enum_variant_missing.ron

Failed in:
  variant ChangeError::TooShort, previously in file /tmp/.tmpgqXWEy/rust-cktap/src/error.rs:134
  variant ChangeError::TooLong, previously in file /tmp/.tmpgqXWEy/rust-cktap/src/error.rs:136
  variant ChangeError::TooShort, previously in file /tmp/.tmpgqXWEy/rust-cktap/src/error.rs:134
  variant ChangeError::TooLong, previously in file /tmp/.tmpgqXWEy/rust-cktap/src/error.rs:136

--- failure pub_module_level_const_missing: pub module-level const is missing ---

Description:
A public const is missing or renamed
        ref: https://doc.rust-lang.org/cargo/reference/semver.html#item-remove
       impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.50.0/src/lints/pub_module_level_const_missing.ron

Failed in:
  CVC in file /tmp/.tmpgqXWEy/rust-cktap/src/emulator.rs:15

Changelog

0.4.0 - 2026-09-21

Other

• Preserve typed errors across the FFI
• Preserve typed APDU errors
• Harden CVC authentication flows

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This PR was generated with release-plz.

[notmandatory]

I'll refresh this PR and finish the release after #71 is merged unless anyone needs a release sooner.