Fix struct field does not handle custom serializers

[fzyzcjy]

Changes

Close #2212
Close #2201

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 98.43750% with 1 line in your changes missing coverage. Please review.

Project coverage is 98.95%. Comparing base (5608d3d) to head (2e0afc0).
Report is 33 commits behind head on master.

Files with missing lines	Patch %	Lines
...degen/src/library/codegen/ir/mir/custom_ser_des.rs	80.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2294   +/-   ##
=======================================
  Coverage   98.94%   98.95%           
=======================================
  Files         491      492    +1     
  Lines       20289    20313   +24     
=======================================
+ Hits        20075    20100   +25     
+ Misses        214      213    -1     

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