Let reconnect preserve session state

[rolandwalker]

Description

Followups to reconnect() refactor:

• Before attempting sqlexecute.connect(), try ping(reconnect=True) to do a true reconnect, preserving the connection_id() and other state such as session variables. This is the important part, which the commentary calls the "second pass".
• Also, before attempting ping(reconnect=True), try ping(reconnect=False) with fewer feedback messages, which the commentary calls the "first pass". This pass is helpful to keep chatter down when the user habitually chooses the "connect" verb over "use".
• Add new explicit feedback around creating a new connection when doing so, including a red tip to the user that session state was lost.
• Tweak docstring in manual_reconnect() eg: "real function" -> "utility method"
• Move db-change logic out of utility method, into manual_reconnect() and change_db(), keeping the database optional argument, as it is still useful for finessing feedback messages.
• Silently skip changing the database if it equals "``".
• In the usual case, let manual_reconnect() yield the result of change_db(), leaving us directly hooked in to the 4-tuple return-value system (instead of iterating on change_db() internally and manually handling the echo()).
• Add an assert on self.sqlexecute.conn before pinging it.
• Clarify "database" vs "server" in reconnect() docstring. (Pedantically it could be "cluster" or "endpoint").
• Update changelog, but just piggyback two words onto the previous entry.
• Update tests to use mycli.packages.special.execute() rather than CliRunner(). CliRunner() is only capable of testing the first line of output, which is taken up by an initialization statement.

xref #1416

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 run ruff check && uv run ruff format && uv run mypy --install-types . to lint and format the code.