FIX: Fix precision loss when binding large Decimal values to SQL_NUMERIC_STRUCT (#287)

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[AB#38111](https://sqlclientdrivers.visualstudio.com/c6d89619-62de-46a0-8b46-70b92a84d85e/_workitems/edit/38111)

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This pull request significantly improves the handling of SQL Server
NUMERIC/DECIMAL values in both the Python and C++ layers, addressing
precision, scale, and binary representation for high-precision decimals.
It also introduces a comprehensive suite of tests to validate numeric
roundtrip, edge cases, and boundary conditions. The changes ensure
compliance with SQL Server's maximum precision (38 digits), robust
conversion between Python decimals and SQL binary formats, and better
test coverage for numeric types.

* The `_get_numeric_data` method in `cursor.py` now correctly calculates
the binary representation of decimal values, supporting up to 38 digits
of precision, and constructs the byte array for SQL Server
compatibility. The restriction on precision is raised from 15 to 38
digits.
[[1]](diffhunk://#diff-deceea46ae01082ce8400e14fa02f4b7585afb7b5ed9885338b66494f5f38280L198-R199)
[[2]](diffhunk://#diff-deceea46ae01082ce8400e14fa02f4b7585afb7b5ed9885338b66494f5f38280L218-R223)
[[3]](diffhunk://#diff-deceea46ae01082ce8400e14fa02f4b7585afb7b5ed9885338b66494f5f38280L232-R251)
* The C++ `NumericData` struct now stores the value as a binary string
(16 bytes) instead of a 64-bit integer, allowing support for
high-precision numerics. Related memory handling is updated for
parameter binding.
[[1]](diffhunk://#diff-dde2297345718ec449a14e7dff91b7bb2342b008ecc071f562233646d71144a1R24)
[[2]](diffhunk://#diff-dde2297345718ec449a14e7dff91b7bb2342b008ecc071f562233646d71144a1L59-R65)
[[3]](diffhunk://#diff-dde2297345718ec449a14e7dff91b7bb2342b008ecc071f562233646d71144a1L560-R564)
[[4]](diffhunk://#diff-dde2297345718ec449a14e7dff91b7bb2342b008ecc071f562233646d71144a1L2055-R2065)
[[5]](diffhunk://#diff-dde2297345718ec449a14e7dff91b7bb2342b008ecc071f562233646d71144a1L3797-R3801)

* Old numeric tests were removed and replaced with a new, thorough set
of tests covering roundtrip for basic, high-precision, negative, zero,
small, boundary, NULL, fetchmany, and executemany scenarios for numeric
values. This ensures that all critical cases are validated.
[[1]](diffhunk://#diff-82594712308ff34afa8b067af67db231e9a1372ef474da3db121e14e4d418f69L1643-L1658)
[[2]](diffhunk://#diff-82594712308ff34afa8b067af67db231e9a1372ef474da3db121e14e4d418f69L1724-L1765)
[[3]](diffhunk://#diff-82594712308ff34afa8b067af67db231e9a1372ef474da3db121e14e4d418f69R11348-R11564)

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These changes collectively make the library more robust and compliant
with SQL Server's numeric type requirements, and the expanded tests will
help catch future regressions.
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Author: gargsaumya