Rename PersistedError::error_state to fatal_state

[xstoicunicornx]

The method returns the state carried by a fatal rejection, mirroring transient_state for transient ones. Name it after the error class it applies to so the pairing is clear at the call site.

This is a follow up I suggested from #1724 (comment), feel free to close if not taking.

Claude Fable was used to generate these updates.

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[coveralls]

Coverage Report for CI Build 29125015849

Coverage remained the same at 86.01%

Details

• Coverage remained the same as the base build.
• Patch coverage: 1 uncovered change across 1 file (5 of 6 lines covered, 83.33%).
• No coverage regressions found.

Uncovered Changes

File	Changed	Covered	%
payjoin-cli/src/app/v2/mod.rs	1	0	0.0%
Total (3 files)	6	5	83.33%

Coverage Regressions

No coverage regressions found.

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Coverage Stats

Relevant Lines:	15876
Covered Lines:	13655
Line Coverage:	86.01%
Coverage Strength:	343.76 hits per line

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💛 - Coveralls

[spacebear21]

concept ACK

[caarloshenriq]

ACK 199b96e