Look up RK instead of looping

[benalleng]

Follow up from #995. We can replace a loop over all active session ids with a WHERE clause.

Supersedes #1013

since this helper function returns a Result<Option<SessionId>> I opted to move some match error handing within the function itself instead of matching at the send_payjoin level

Additionally adds some enhacements suggested from the original PR like adding "completed_at IS NULL"

Pull Request Checklist

Please confirm the following before requesting review:

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  AI
  in the body of this PR.
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[coveralls]

Coverage Report for CI Build 28665120300

Coverage decreased (-0.04%) to 85.899%

Details

• Coverage decreased (-0.04%) from the base build.
• Patch coverage: 21 of 21 lines across 2 files are fully covered (100%).
• 7 coverage regressions across 1 file.

Uncovered Changes

No uncovered changes found.

Coverage Regressions

7 previously-covered lines in 1 file lost coverage.

File	Lines Losing Coverage	Coverage
payjoin-cli/src/db/v2.rs	7	82.9%

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Coverage Stats

Relevant Lines:	15538
Covered Lines:	13347
Line Coverage:	85.9%
Coverage Strength:	350.88 hits per line

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💛 - Coveralls

[benalleng]

@DanGould I think this PR still has utility even after our upgrade to uuid v7 simply for the sake of code simplification on the sender side.

[DanGould]

Only nits otherwise lgtm ACK 8b7486a

[xstoicunicornx]

utACK 2490ef2

Reviewed changes and tested locally. This is a much more straightforward implementation that avoids unnecessary db calls made by the now unneeded loop.