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[bot]]

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 :warning:

Additional details and impacted files

```diff @@ 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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