feat: promote Trino driver from stub to full implementation

[dtsong]

Problem

trino.py is a 49-line stub extending Presto with minimal overrides. While Presto compatibility covers basic operations, Trino-specific syntax and behavior differences may produce silent incorrect results.

Scope

Full Trino driver implementation with:

• Trino-specific type mappings
• Native timestamp precision handling
• Trino-specific SQL syntax where it diverges from Presto
• Dedicated test file

Depends on: #36 (Trino audit) to identify specific divergence points.

Acceptance Criteria

• Trino driver is a standalone implementation (not a Presto subclass)
• Dedicated test_trino.py test file
• All BaseDialect methods implemented