Copy local implementation

[sivaalamp]

Implemented COPY FROM LOCAL support in the driver by handling the full local-file load protocol over simple query execution.

1. Added LOCAL COPY detection and rewrite flow in stmt.go so COPY ... FROM LOCAL is executed safely without prepared-statement flush/state conflicts.
2. Implemented local file streaming and verification handlers for Vertica load messages (load file chunks, end-of-file, file-size verification, and load-fail responses) in stmt.go.
3. Wired protocol message handling for local load/verify message types already present under msgs.
4. Added integration tests for LOCAL COPY formats in driver_test.go: CSV, JSON (FJSONPARSER), pipe-delimited, TSV, and Avro (FAVROPARSER).
5. Added corresponding test fixtures and SQL setup/teardown scripts under resources, including JSON/PSV/TSV/Avro test data and new pre/post SQL files in driver_test.

[sivaalamp]

go test is ran locally to ensure the added test cases and existing test cases are passed.