Unused dependency flaged by nix check

[Mshehu5]

This PR addresses the following changes:

• Removes the .udl filter from Nix cause ffi layer doesn't use udl files anymore as discussed in the mob review meeting.
• Adds a Machete dependency check to the Nix flake, as referenced in issue nix flake tracking issue #457
• Removes dependencies flagged as unused by Machete

Note: I kept getrandom because the wasm_js feature requires getrandom/js so it’s an actual dependency.
If you remove it and run cargo check you’ll see this.

After adding machete check I ran nix flake check which displayed the log below

❌ checks.x86_64-linux.payjoin-workspace-machete
error: Cannot build '/nix/store/qfx7v13m73iq8v4b0izi7260xdd5hx15-payjoin-workspace-machete-no-version.drv'.
       Reason: builder failed with exit code 1.
       Output paths:
         /nix/store/lwvvwfbhnfqkmh1rzp46l9rv8l33s4yv-payjoin-workspace-machete-no-version
       Last 25 log lines:
       >        futures
       >         hyper-rustls
       >    rcgen
       >   sled
       > payjoin-test-utils -- ./payjoin-test-utils/Cargo.toml:
       >     log
       > payjoin-ffi -- ./payjoin-ffi/Cargo.toml:
       >    base64
       >  getrandom
       >       hex
       > payjoin-ffi-wrapper -- ./payjoin-ffi/dart/native/Cargo.toml:
       >        home
       >
       > If you believe cargo-machete has detected an unused dependency incorrectly,
       > you can add the dependency to the list of dependencies to ignore in the
       > `[package.metadata.cargo-machete]` section of the appropriate Cargo.toml.
       > For example:
       >
       > [package.metadata.cargo-machete]
       > ignored = ["prost"]
       >
       > You can also try running it with the `--with-metadata` flag for better accuracy,
       > though this may modify your Cargo.lock files.
       >
       > Done!

Second time running after removing dependencies I got the error below. It did not catch this in the first check :

❌ checks.x86_64-linux.payjoin-workspace-machete
error: Cannot build '/nix/store/ymsycgba5z2vw53x3ibrf081fwys464a-payjoin-workspace-machete-no-version.drv'.
       Reason: builder failed with exit code 1.
       Output paths:
         /nix/store/lz9a60g9wfkjrmmyjn164z7n1sr1sck2-payjoin-workspace-machete-no-version
       Last 25 log lines:
       > Running phase: configurePhase
       > will append /build/source/.cargo-home/config.toml with contents of /nix/store/whmqvxdpvzjqzzjb38djwznb5fm9qv63-vendor-cargo-deps/config.toml
       > default configurePhase, nothing to do
       > Running phase: buildPhase
       > +++ command cargo --version
       > cargo 1.93.0-nightly (bd979347d 2025-12-02)
       > Running phase: checkPhase
       > +++ command cargo machete
       > Analyzing dependencies of crates in this directory...
       > cargo-machete found the following unused dependencies in this directory:
       > payjoin-directory -- ./payjoin-directory/Cargo.toml:
       >     hyper-rustls
       >

Pull Request Checklist

Please confirm the following before requesting review:

• I have disclosed my use of
  AI
  in the body of this PR.
• I have read CONTRIBUTING.md and rebased my branch to produce hygienic commits.

[coveralls]

Pull Request Test Coverage Report for Build 20144561401

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 83.176%

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Totals
Change from base Build 20141275772:	0.0%
Covered Lines:	9665
Relevant Lines:	11620

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💛 - Coveralls

[benalleng]

Could you explain why this is necessary here instead of a removal?

[Mshehu5]

Yeah, I kept getrandom because the wasm_js feature requires getrandom/js so it’s an actual dependency.
If you remove it and run cargo check you’ll see this.

[spacebear21]

Perhaps this exclusion should be explained in a code comment here

[spacebear21]

extra line

[spacebear21]

Nice! I have some very minor comments but otherwise lgtm

[benalleng]

Ack fe4858c