fix: add VERSION to builtin function completion

[devadathanmb]

Description

Adds VERSION to pgcli's builtin function completion list so SELECT VERSION(); is suggested during autocompletion.

Closes #1510

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[Copilot]

Pull request overview

Adds the PostgreSQL built-in VERSION function to pgcli’s function completion list so SELECT VERSION(); is suggested during autocompletion (closes #1510).

Changes:

• Add VERSION to the built-in functions literals list.
• Add smart- and naive-completion test coverage for VERSION suggestions.
• Document the fix in the changelog.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
tests/test_smart_completion_public_schema_only.py	Adds a smart-completion regression test ensuring VERSION is suggested for SELECT VE.
tests/test_naive_completion.py	Adds a naive-completion regression test ensuring VERSION is suggested for SELECT VE.
pgcli/packages/pgliterals/pgliterals.json	Adds VERSION to the built-in functions literal list used by the completer.
changelog.rst	Notes the bug fix in the “Upcoming (TBD)” section.

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