Allow cancel on closed sessions to reprint fallback tx

[benalleng]

Closes #1605

This adds the ability to run cancel on already closed sessions to re-print the fallback tx to be broadcast. This addresses a failure state where a closed session could not access its fallback tx if it was not automatically broadcast.

Coded with help from GLM-5.2

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[coveralls]

Coverage Report for CI Build 28064211352

Coverage decreased (-0.01%) to 85.194%

Details

• Coverage decreased (-0.01%) from the base build.
• Patch coverage: 8 uncovered changes across 2 files (18 of 26 lines covered, 69.23%).
• 2 coverage regressions across 1 file.

Uncovered Changes

File	Changed	Covered	%
payjoin-cli/src/app/v2/mod.rs	8	2	25.0%
payjoin-cli/src/db/v2.rs	18	16	88.89%

Coverage Regressions

2 previously-covered lines in 1 file lost coverage.

File	Lines Losing Coverage	Coverage
payjoin-cli/src/app/v2/mod.rs	2	50.66%

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Coverage Stats

Relevant Lines:	14771
Covered Lines:	12584
Line Coverage:	85.19%
Coverage Strength:	369.67 hits per line

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💛 - Coveralls