Typehint most of main.py, with consequent fixes elsewhere

[rolandwalker]

Description

• typehint >80% of main.py
• requiring additional hints and fixes in config.py and sqlexecute.py, packages/parseutils.py, and others
• typehint unhinted portions of sqlexecute.py
• remove @export decorator and import explicitly into special
• recast some uninformative variable names
• assert that a connection is available before using it
• take more care with: ssl config, port, and ssh_port types/defaults before creating a connection
• local_infile is a boolean, not a string
• ensure get_password_from_file() returns a value
• assert that a PromptSession is available before invoking methods on it
• set a fallback col/row size in case a prompt session is not available
• declare and type self.conn in SQLExecute much earlier
• take more care to distinguish falsey values from Nones in SQLExecute connect()
• improve defaults passed to pymysql.connect(), matching them to the pymysql docs
• test that self.conn is not None rather than checking for a conn attribute, before invoking close()
• remove Python 2.x-compat Unicode literals trick for click
• better catch empty database names in change_db()
• take more care for edge-case values of text in one_iteration()
• don't return None for connection_id_to_kill
• clarify overlapping e variables
• don't use self.sqlexecute when sqlexecute is already available
• is_dropping_database() takes a string, not a list
• typehint unhinted function in packages/parseutils.py
• use only chain() for format_output() output
• test isinstance(…, Cursor) rather than hasattr(…, "description")
• set start = time() before try block
• update changelog

@amjith I tried to keep the cute @export decorator but it is too dynamic for a static checker to understand.

Checklist

• I've added this contribution to the changelog.md.
• I've added my name to the AUTHORS file (or it's already there).
• I ran uv ruff check && uv ruff format to lint and format the code.

[amjith]

Non-blocking question. Do you think we need to hoist all these functions to the top level?

BTW, I'm fine with removing the @export decorator.

[rolandwalker]

I don't think we do need to hoist. It could be nicer not to.