[junkmd]

Motivation

comtypes has problems with fixed-point numbers (VT_CY and VT_DECIMAL).

Current problems:

• VT_CY uses c_longlong for internal storage. This is not correct because VT_CY should use tagCY structure.
• When sending Decimal values, the code uses int(round(value * 10000)) which silently truncates large values and rounds without warning.
• The calculation uses global decimal context, so getcontext().prec changes the result.
• There is no way to send VT_DECIMAL type.
• The _ctype_to_vartype dictionary is missing VT_CY and VT_DECIMAL entries.
• SAFEARRAY did not support tagCY or tagDEC types, so fixed-point numbers could not be used in arrays.

Summary

This PR fixes the fixed-point number marshaling.
SAFEARRAY now supports tagDEC and tagCY, and preserves the correct type when the internal storage of a VARIANT is VT_CY.
Implicit rounding when passing a Decimal to a VARIANT parameter has been maintained. Keeping this behavior unchanged for now as it fall under Hyrum's Law.

Changes

Changed Behavior

• VT_CY internal representation: The private union field v._.VT_CY now uses tagCY structure instead of c_longlong. This is an internal change only (accessed via v._.VT_CY).
• Dictionary completeness: _ctype_to_vartype now includes tagCY: VT_CY and tagDEC: VT_DECIMAL mappings.
• SAFEARRAY support: SAFEARRAY(tagCY) and SAFEARRAY(tagDEC) can now be created and unpacked. Unpacking returns Decimal values for easier use.

Not Changed

• Public API: VARIANT.value property setter behavior for Decimal values is unchanged
• tagDEC.as_decimal() behavior unchanged

Internal Changes

• v._.VT_CY is now a tagCY structure, not c_longlong. Code accessing this private attribute directly will need to use .int64 property.
• _vartype_to_ctype and _ctype_to_vartype updated for VT_CY and VT_DECIMAL.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 99.52267% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.33%. Comparing base (3bf33b2) to head (302d7f0).

Files with missing lines	Patch %	Lines
comtypes/test/test_fixed_point_numbers.py	98.26%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #978      +/-   ##
==========================================
+ Coverage   90.05%   90.33%   +0.27%     
==========================================
  Files         143      145       +2     
  Lines       14152    14567     +415     
==========================================
+ Hits        12745    13159     +414     
- Misses       1407     1408       +1     

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