fix(sqlalchemy): add literal_processor to TIMESTAMP type

[q8webmaster]

Problem

TIMESTAMP.literal_processor() is not implemented, causing a CompileError when
literal_binds=True is used with a datetime.datetime value in a WHERE clause:

sqlalchemy.exc.CompileError: No literal value renderer is available for literal value
"datetime.datetime(2026, 6, 17, 9, 57, 43, 244000)" with datatype DATETIME

Concrete trigger: Apache Superset's select_star() builds a sample query with
WHERE <partition_col> = <latest_partition_value> using literal_binds=True. Any
table with a TIMESTAMP partition column hits this on the table metadata endpoint.

Fix

Add literal_processor to TIMESTAMP emitting a Trino-compatible
TIMESTAMP 'YYYY-MM-DD HH:MM:SS[.mmm]' literal.

Tests

Two unit tests added to tests/unit/sqlalchemy/test_compiler.py:

• datetime with sub-second precision → TIMESTAMP '2026-06-17 09:57:43.244'
• datetime without microseconds → TIMESTAMP '2026-06-17 09:57:43'

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