fix(fabric): widen tinyint integer precision to smallint

[sdebruyn]

Fixes #4306

Summary

• Override to_db_integer_type in FabricTypeMapper so a bigint column with precision <= 8 maps to smallint instead of tinyint
• Copy the column before adjusting it, so the widening does not leak back into the caller's schema

Root cause

Fabric Warehouse has no tinyint; smallint is its narrowest integer type. sql_database reflects a SQL Server TINYINT as dlt type bigint with precision=8, and MsSqlTypeMapper.to_db_integer_type maps that to tinyint. FabricTypeMapper inherits that through SynapseTypeMapper and previously overrode only the datetime and string mappings, so CREATE TABLE failed with a DatabaseTerminalException. Being terminal, the load was not retried and every subsequent run failed on the same table.

Widening is safe: TINYINT values (0-255) all fit in smallint. Nothing changes for mssql or synapse, where tinyint is valid.

Test plan

• Added test_fabric_type_mapper_integer_precision, parametrized over no precision, 8, 16, 32 and 64, asserting bigint, smallint, smallint, int, bigint. It also asserts the input column is left untouched.
• Verified on devel before the change that precision 8 yields tinyint, so the test is a real regression guard.
• tests/load/fabric: 20 passed, 1 skipped (the table builder module skips without an ODBC driver).
• mypy, ruff, flake8 (including the docstring pass over impl/**/factory.py) and black all clean.