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

[codecov[bot]]

Codecov Report

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

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

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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