Remove stale incompatible_msrv suppressions

[DanGould]

Summary

• Removed 4 #[allow(clippy::incompatible_msrv)] attributes from payjoin-cli that are no longer needed

Closes payjoin#794

Test plan

• nix fmt -- --ci passes
• cargo clippy --all-targets --keep-going --all-features -- -D warnings clean
• codespell clean
• CI passes on fork

Disclosure: co-authored by Claude

[coveralls]

Pull Request Test Coverage Report for Build 22572331810

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 82.484%

---

Totals
Change from base Build 22572195695:	0.0%
Covered Lines:	10624
Relevant Lines:	12880

---

💛 - Coveralls

[coderabbitai]

Important

Review skipped

Draft detected.

Please check the settings in the CodeRabbit UI or the .coderabbit.yaml file in this repository. To trigger a single review, invoke the @coderabbitai review command.

You can disable this status message by setting the reviews.review_status to false in the CodeRabbit configuration file.

Use the checkbox below for a quick retry:

• 🔍 Trigger review

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch fix/794-msrv-clippy

---

_{Comment @coderabbitai help to get the list of available commands and usage tips.}