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Superseded by #1424 (merged to staging as 78243c3).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