feat: add typed enums and allow type-specifier to be suffixed

[mhasel]

Add support for typed enums with explicit integer type specifications, supporting both IEC 61131-3 standard syntax (TYPE NAME : TYPE (...)) and Codesys syntax (TYPE NAME : (...) TYPE).

Additionally, enums are no longer blanket-zero-initialized but rather they will:

1. be initialized with an explicit initializer (if present)
2. be initialized with the 0 variant (if present)
3. fall back to the first declared variant

[mhasel]

Design Question: Should finalize_enum_defaults() be integrated into evaluate_constants()?

Currently, finalize_enum_defaults() is called separately after evaluate_constants() in three places:

• Main pipeline (pipelines.rs)
• Test utilities (test_utils.rs, 2 locations)

Arguments for keeping them separate (current approach):

• Clear separation of concerns: Constant evaluation and enum initialization are conceptually distinct operations
• Modularity: Each function has a single, well-defined responsibility
• Explicit pipeline: Makes it obvious what post-resolution steps are needed

Arguments for integrating into evaluate_constants():

• Strong dependency: finalize_enum_defaults() fundamentally requires resolved constants and cannot work without them
• Simpler API: Single function call instead of remembering to call both in sequence
• Maintenance: Reduces chance of forgetting this pass in new code paths
• Logical cohesion: Both operations finalize constant-related initialization

Should we consider renaming to something like resolve_constants_and_initializers() or updating the evaluate_constants() doc comment to clarify it also handles dependent initialization steps and add this pass to evaluate_constants()?

[codecov]

Codecov Report

❌ Patch coverage is 99.42529% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 95.01%. Comparing base (ce68921) to head (d34959b).
⚠️ Report is 36 commits behind head on master.

Files with missing lines	Patch %	Lines
src/index.rs	96.55%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1544      +/-   ##
==========================================
+ Coverage   94.03%   95.01%   +0.98%     
==========================================
  Files         174      175       +1     
  Lines       58611    56206    -2405     
==========================================
- Hits        55112    53406    -1706     
+ Misses       3499     2800     -699     

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