Feat/341/rework password logic

[scottnemes]

Description

Updates the password handling functionality as follows:

1. Add ability to use the -p flag to launch a password prompt (or to enter cleartext as before)
2. Check for -p flag at the earliest possible point to reduce prompt load time (still limited by startup time)
3. Allow for an empty string password from the envvar MYSQL_PWD
4. Clarify password option hierachy:
   1. -p / --pass/--password CLI options
   2. envvar (MYSQL_PWD)
   3. DSN (mysql://user:password)
   4. cnf (.my.cnf / etc)
   6. --password-file CLI option
5. Removes password prompt logic from the reconnect logic to reduce redundancy. Reconnections should still work fine from testing.

Closes #341

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.

[scottnemes]

@rolandwalker
The two points from the original issue were basically:

1. Get a password prompt to the user faster
2. Make -p open a prompt like the vendor client does

For the first point, this moves the -p logic to the earliest possible place. It's at best a minuscule amount faster, but barely noticeable. The majority of the delay is the "startup" time, which just takes a bit. But with this, any improvements we do make in the future to speed up the startup time will further reduce the time until password prompt.

For the second point, -p will now be usable by itself (just -p) to open a password prompt. It can also be used to enter the password in cleartext, like "-pMYPASS or -p MYPASS". That is the one difference with the vendor client; with the vendor client you can't do "-p MYPASS" as it treats the value as the DB when there is a space in between. I could not duplicate that functionality with click. I don't believe that's a big deal, but wanted to point it out anyway.