This is a backport of the PR duckdb#177 to `v1.3-ossivalis` stable branch.

This change addresses multiple ODBC specification conformance issues discovered
during a thorough audit of GetColumnSize() and GetDisplaySize() implementations.

Issues fixed:
1. DECIMAL/NUMERIC precision and scale reporting
    - SQLColAttribute/SQLDescribeCol incorrectly reported column sizes
    - Fixed GetColumnSize() to return precision instead of precision+scale

2. Signed/Unsigned integer display sizes
    - GetDisplaySize() now correctly distinguishes signed vs unsigned types
    - UTINYINT: 3 chars, USMALLINT: 5 chars, UINTEGER: 10 chars, UBIGINT: 20 chars
    - TINYINT: 4 chars, SMALLINT: 6 chars, INTEGER: 11 chars, BIGINT: 20 chars

3. TIME/TIMESTAMP fractional seconds precision
    - Added GetTemporalPrecision() to detect precision from LogicalTypeId
    - Added missing type mappings for TIMESTAMP_MS, TIMESTAMP_SEC, TIMESTAMP_NS
    - Fixed GetColumnSize() to return full column size per ODBC spec:
    * TIME: 8 (base) or 9 + precision
    * TIMESTAMP: 19 (base) or 20 + precision
    - Fixed GetDisplaySize() to include fractional seconds in display size
    - Updated FillIRD() and SQLDescribeCol to set precision/scale for temporal types

Implementation details:
- include/api_info.hpp: Added GetTemporalPrecision(), updated size calculations
- src/api_info.cpp: Added missing timestamp variant type mappings
- src/common/duckdb_odbc.cpp: Set temporal precision/scale in IRD
- src/prepared.cpp: Handle temporal types in SQLDescribeCol
- test/: Added comprehensive test coverage for all fixes

All changes verified against DuckDB behavior and ODBC specification.
All 79 tests passing with new test coverage added.