feat: expose detailed try_finalize_psbt outcomes

[reez]

Description

First step for #73, following ValuedMammal's suggestion.

This PR keeps the scope to PSBT finalization only:

• add try_finalize_psbt which returns FinalizePsbtResult
• report per input outcomes via FinalizePsbtInputResult

Notes to the reviewers

This is now additive rather than breaking: Wallet::finalize_psbt still returns bool

Intentionally not included here:

• changing Wallet::sign to return a richer result type
• any broader redesign beyond the PSBT finalization API surface

Changelog notice

• Add Wallet::try_finalize_psbt, which returns FinalizePsbtResult and exposes per-input finalization outcomes while preserving the existing Wallet::finalize_psbt API.

Checklists

All Submissions:

• I've signed all my commits
• I followed the contribution guidelines
• I ran just p before pushing

New Features:

• I've added tests for the new feature
• I've added docs for the new feature

[codecov]

Codecov Report

❌ Patch coverage is 96.38554% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 81.13%. Comparing base (58fe631) to head (653031a).

Files with missing lines	Patch %	Lines
src/wallet/mod.rs	96.38%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #433      +/-   ##
==========================================
+ Coverage   80.96%   81.13%   +0.17%     
==========================================
  Files          24       24              
  Lines        5489     5546      +57     
  Branches      247      246       -1     
==========================================
+ Hits         4444     4500      +56     
- Misses        968      970       +2     
+ Partials       77       76       -1     

Flag	Coverage Δ
rust	81.13% <96.38%> (+0.17%)	⬆️

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[reez]

Updated per some good feedback from mammal

[ValuedMammal]

I don't think After and Older are doing much good, and would prefer to leave them out of the new implementation if we plan to support try_finalize_psbt into the future.

[notmandatory]

Concept ACK, glad to see this as a non-breaking change.

[reez]

Added four commits as small follow-ups from review feedback from mammal: make finalization cleanup more explicit, preserve opaque PSBT/input metadata, stop the new try_finalize_psbt path from redacting output metadata, and clarify the internal timelock inputs without changing legacy finalize_psbt behavior.