perf: lazy-load generated filter cache on startup

[jaromil]

Summary

• stop sourcing $MAILDIRS/cache/filters when loading the filters library
• add load_filter_cache and call it only from filter/sieve paths that need generated filter arrays
• move runtime checks after command parsing and scope them to commands that need keyring, GnuPG, fetchmail, msmtp, or mutt
• remove duplicate colors initialization from bootstrap
• avoid creating/touching the mblaze sequence directory at startup; initialize it lazily before mblaze commands run
• disable mutt's GPGME/S/MIME auto handling by default so attached smime.p7s signatures fail fast instead of blocking message opening
• refresh the GPG agent TTY before invoking pass, so !jaro send from inside mutt can decrypt the stored SMTP password instead of prompting again

Measured locally

• before: installed jaro -q source addr around 20s on the real mailbox
• after lazy filter cache: source-tree jaro -q source addr around 0.05s
• after scoped checks/lazy mblaze: source-tree jaro -q source addr around 0.04s
• source-tree jaro -q -a jaromil@dyne.org askpass remains under 1s

Validation

• make
• zsh extras/test/run-source.sh
• zsh extras/test/test-mutt-crypto.sh
• zsh extras/test/test-filtering.sh
• zsh extras/test/test-sieve-import.sh
• zsh extras/test/test-maildir-commands.sh
• zsh extras/test/test-addressbook-parse.sh
• zsh extras/test/test-account-wizard.sh