* feat(message-buffer): add payer to all contexts requiring lamports for rent
separate admin from payer of account creation/resize/deletion
* test(message-buffer): add test for same admin & payer
* feat(message-buffer/scripts): keep payer & admin the same in init-buffer script for simplicity
* fix(message-buffer): set payer as admin in initialize (TOB-PYTH-5)
* fix(message-buffer/delete_buffer): remove auth validation in delete_buffer & add test (TOB-PYTH-7)
* fix(message-buffer): fix non-security-related findings
use constant for seeds, cap max target size, add more tests
* refactor(message-buffer): use seed consts in initialize, remove unused errors
* refactor(message-buffer): address PR comments
refactor missed consts, make initialize more readable