refactor: introduce payjoin_directory::Service

[nothingmuch]

This is a preparatory change to avoid tight coupling to redis as a storage backend, and to enable ACME support by simplifying the listener logic.

• implements hyper::Service trait
• Arc<Mutexohttp::Server> -> ohttp::Server
• remove serve_payjoin_directory function
• simplify and remove various listen helpers

[spacebear21]

utACK, very nice refactor.

[spacebear21]

ACK c173a25

[coveralls]

Pull Request Test Coverage Report for Build 16725345224

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
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• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 208 of 250 (83.2%) changed or added relevant lines in 3 files are covered.
• 5 unchanged lines in 2 files lost coverage.
• Overall coverage increased (+0.2%) to 86.192%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
payjoin-directory/src/main.rs	0	9	0.0%
payjoin-directory/src/lib.rs	197	230	85.65%

Files with Coverage Reduction	New Missed Lines	%
payjoin-directory/src/main.rs	1	0.0%
payjoin-directory/src/lib.rs	4	67.05%

Totals
Change from base Build 16682297890:	0.2%
Covered Lines:	7996
Relevant Lines:	9277

---

💛 - Coveralls