Fix LOGMECH precedence for DATABASE_URI query params #288

[dtehan-td]

Summary

• Supports LOGMECH (and other query params like ENCRYPTDATA, SSLMODE) specified directly in the DATABASE_URI connection string
• Establishes clear precedence: CLI arg / env var > URI query param > default TD2
• Adds _build_query_string() helper to merge extra URI params into all reconstructed SQLAlchemy URLs (main connection, basic auth validation, JWT auth)

Test plan

• Verify LOGMECH in DATABASE_URI (e.g. teradata://user:pass@host/db?LOGMECH=LDAP) is respected when no --logmech CLI arg or LOGMECH env var is set
• Verify --logmech CLI arg or LOGMECH env var overrides URI LOGMECH
• Verify additional URI query params (e.g. ENCRYPTDATA=ON) are propagated to all connection URLs
• Verify LOGDATA from the original URI is not carried into derived connections

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