Use "expiration" instead of "expiry"

[arminsabouri]

Our codebase goes back and forth between "expiry" and "expiration". Expiry is prefered as its used in BIP-77.

Closes: #1065

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[coveralls]

Pull Request Test Coverage Report for Build 17803250787

Details

• 33 of 34 (97.06%) changed or added relevant lines in 6 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage increased (+0.003%) to 84.681%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
payjoin/src/core/send/v2/error.rs	1	2	50.0%

Files with Coverage Reduction	New Missed Lines	%
payjoin/src/core/receive/v2/mod.rs	1	92.4%

Totals
Change from base Build 17782565042:	0.003%
Covered Lines:	8082
Relevant Lines:	9544

---

💛 - Coveralls

[spacebear21]

ACK e5e548c