Fix: Parametrized bigdecimal mapping was being concatenated with params

[themisvaltinos]

the default BIGDECIMAL to DECIMAL(38, 5) mapping was being concatenated with explicit (76, 38) params, producing DECIMAL(38, 5)(76, 38) in ducked:

DECLARE x DECIMAL(38, 5)(76, 38)

added a check in _datatype_sql to pass through the usersupplied params when present instead and falling back to the default otherwise

[github-actions]

SQLGlot Integration Test Results

Comparing:

• this branch (sqlglot:themis/bigdec, sqlglot version: themis/bigdec)
• baseline (main, sqlglot version: 0.0.1.dev1)

By Dialect

dialect	main	sqlglot:themis/bigdec	transitions	links
bigquery -> bigquery	24647/24652 passed (100.0%)	24647/24652 passed (100.0%)	No change	full result / delta
bigquery -> duckdb	867/1154 passed (75.1%)	867/1154 passed (75.1%)	No change	full result / delta
duckdb -> duckdb	5823/5823 passed (100.0%)	5823/5823 passed (100.0%)	No change	full result / delta
snowflake -> duckdb	1063/1961 passed (54.2%)	0/0 passed (0.0%)	Results not found	full result / delta
snowflake -> snowflake	65133/65133 passed (100.0%)	63027/63027 passed (100.0%)	No change	full result / delta
databricks -> databricks	1370/1370 passed (100.0%)	1370/1370 passed (100.0%)	No change	full result / delta
postgres -> postgres	6042/6042 passed (100.0%)	6042/6042 passed (100.0%)	No change	full result / delta
redshift -> redshift	7101/7101 passed (100.0%)	7101/7101 passed (100.0%)	No change	full result / delta

Overall

main: 113236 total, 112046 passed (pass rate: 98.9%), sqlglot version: 0.0.1.dev1

sqlglot:themis/bigdec: 109169 total, 108877 passed (pass rate: 99.7%), sqlglot version: themis/bigdec

Transitions:
No change

Dialect pair changes: 0 previous results not found, 1 current results not found

✅ 38 test(s) passed