chore(xelis): bump xelis_flutter to master HEAD + xelis_dart_sdk 0.31.0

[danrmiller]

No description provided.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 4.75%. Comparing base (c6a2308) to head (cf8ff9e).
⚠️ Report is 1 commits behind head on staging.

Additional details and impacted files

@@             Coverage Diff              @@
##           staging    #1423       +/-   ##
============================================
- Coverage    74.00%    4.75%   -69.25%     
============================================
  Files           12     1108     +1096     
  Lines          704   110815   +110111     
============================================
+ Hits           521     5273     +4752     
- Misses         183   105542   +105359     

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[danrmiller]

Superseded by #1424 (merged to staging as 78243c3).

Both pins this PR raised have since been taken further on staging:

• xelis_dart_sdk 0.30.9 -> 0.31.0 here; staging is now 0.35.1. 0.31.0 was a cap imposed by json_serializable 6.11.2 pinning json_annotation <4.10.0, which was only in the graph because the cypherstack/tezart fork listed that codegen tool as a runtime dep. Fixed upstream in tezart as 84c56310, which lifted the cap without any codegen-toolchain realignment.
• xelis_flutter v0.2.1 -> f67a02c here; staging is now 3e5ac06c (past f67a02c, and off the floating branch = "dev" Rust dep).

The pubspec.lock here has also gone stale and carries unrelated regressions (cs_salvium_flutter_libs and its platform packages downgraded 3.x -> 2.x, coinlib/coinlib_flutter and flutter_libsparkmobile pointing at refs staging does not use), so it is not mergeable as-is.

Nothing depends on the branch, so deleting it. The commit and diff stay accessible on this PR.