Add #[frb(type_64bit_int)] to pick preferred Dart big integer type

[fzyzcjy]

Changes

Close #2035

Checklist

• An issue to be fixed by this PR is listed above.
• New tests are added to ensure new features are working. Please refer to this page to see how to add a test.
• ./frb_internal precommit --mode slow (or fast) is run (it internal runs code generator, does auto formatting, etc).
• If this PR adds/changes features, documentations (in the ./website folder) are updated.
• CI is passing. Please refer to this page to see how to solve a failed CI.

Remark for PR creator

• ./frb_internal --help shows utilities for development.
• If fzyzcjy does not reply for a few days, maybe he just did not see it, so please ping him.

[codecov]

Codecov Report

Attention: Patch coverage is 96.51163% with 3 lines in your changes missing coverage. Please review.

Project coverage is 99.07%. Comparing base (918a23c) to head (be2d54f).

Files	Patch %	Lines
...st/spec_generator/codec/cst/decoder/ty/delegate.rs	0.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2065      +/-   ##
==========================================
- Coverage   99.08%   99.07%   -0.01%     
==========================================
  Files         471      471              
  Lines       18615    18693      +78     
==========================================
+ Hits        18445    18521      +76     
- Misses        170      172       +2     

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