Add warning when sending credentials over HTTP

[hashhar]

Description

Adds warning when sending credentials over HTTP. JDBC actually disallows this entirely but it can be a breaking change for Python client now.

Non-technical explanation

Release notes

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* Fix some things. ({issue}`issuenumber`)

[Copilot]

Pull request overview

Adds a runtime warning when authentication is configured while using an insecure HTTP connection, to help prevent accidental credential exposure.

Changes:

• Emit a UserWarning in Connection.__init__ when auth is set and the resolved scheme is HTTP.
• Add unit tests asserting the warning is produced for HTTP and not produced for HTTPS.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
trino/dbapi.py	Adds warning emission when auth is used over HTTP.
tests/unit/test_dbapi.py	Adds/updates tests to validate the new warning behavior.

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