fix(lang-v2): honor wincode enum tags in idl and init space

[0x4ka5h]

Finding
InitSpace and enum IDL generation assumed one-byte enum tags, dropping custom wincode tag encodings and per-variant tag values.

Fix
This PR honors wincode(tag_encoding = ...) and variant #[wincode(tag = ...)] metadata in sizing and generated enum IDL. Added regression tests for custom tag encodings and tags.

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[swaroop-osec]

@0x4ka5h please address the failed tests.

[codecov-commenter]

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Codecov Report

❌ Patch coverage is 32.48408% with 106 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (anchor-next@e056cc1). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
lang-v2/derive/src/wincode_attrs.rs	35.08%	37 Missing ⚠️
lang-v2/derive/src/lib.rs	27.08%	35 Missing ⚠️
lang-v2/derive/src/idl.rs	0.00%	17 Missing ⚠️
lang-v2/derive/src/init_space.rs	45.16%	17 Missing ⚠️
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Additional details and impacted files

@@              Coverage Diff               @@
##             anchor-next    #4819   +/-   ##
==============================================
  Coverage               ?   63.29%           
==============================================
  Files                  ?      127           
  Lines                  ?    13806           
  Branches               ?        0           
==============================================
  Hits                   ?     8738           
  Misses                 ?     5068           
  Partials               ?        0           

Flag	Coverage Δ
v2	63.29% <32.48%> (?)

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