fix: skip startup cursor query

[AbhiTheModder]

When ratatui 0.30's terminal.clear() was called right after entering alternate screen mode, the internal get_cursor_position() call sent a `\x1b[6n` (DSR) query that arrived before crossterm's event system was ready, causing a timeout and the raw response ^[[1;1R to appear on screen. Replace it with clear_region(ClearType::All) on the backend directly, which skips the unnecessary cursor save/restore at this point in the startup sequence.

[AbhiTheModder]

just in case, below is the error that happens:

╰─> leaf test.md
^[[1;1RError: The cursor position could not be read within a normal duration

[RivoLink]

Hi,
Thank you for your interest in the project and for this PR.

I have a few requests:

• Fix the CI check failure, may be: fix: skip startup cursor query
• GPG signing is required on the main branch, so if you can sign it, great. If not, no worrie, I'll handle it while preserving you as the author.

GPG signing docs : https://docs.github.com/en/authentication/managing-commit-signature-verification/signing-commits

Thanks!

[AbhiTheModder]

Hi @RivoLink,

1. Done, thanks :)
2. Didn't saw anywhere in contributing docs about that, well I lose my keys a lot so I have left using gpg keys, would appreciate it you doing so :)

[RivoLink]

Hi,
Thank you so much!

I’ve signed the commit.
You’re right, I forgot to mention GPG signing in CONTRIBUTING.md. I’ll add it.

Thanks again for this PR, I really appreciate it!