feat: Add support for transaction status indicator (\T) in prompt #1553

[devadathanmb]

Description

Adds support for displaying transaction status in the prompt via the \T escape sequence, similar to psql's %x

Behavior:

• * — inside a valid transaction block
• ! — inside a failed transaction block
• ? — connection is closed/indeterminate
• (empty) — idle, not in a transaction

Example usage in ~/.config/pgcli/config:

prompt = '\u@\h:\d>\T '

This produces prompts like (as shown in the attached screenshot below):

user@localhost:mydb>  SELECT 1;      -- idle

user@localhost:mydb>* BEGIN;         -- in transaction

user@localhost:mydb>! ...            -- failed transaction

user@localhost:mydb>? ...            -- if connection is closed

NOTE: Uses \T instead of \x to avoid conflicts with ANSI escape sequences (\x1b) processing done in the codebase.

Checklist

• I've added this contribution to the changelog.rst.
• I've added my name to the AUTHORS file (or it's already there).

• I installed pre-commit hooks (pip install pre-commit && pre-commit install).
• Please squash merge this pull request (uncheck if you'd like us to merge as multiple commits)