preexec: set options before load

By setting `__bp_delay_install`, we avoid any immediate initialization at all. We then override two troublesome functions before calling `__bp_install_after_session_init()`.

The `__bp_install_after_session_init()` function doesn't enable the DEBUG trap, just sets `$PROMPT_COMMAND` to include `__bp_install()`, so the actual final `$PROMPT_COMMAND` is not finished, and DEBUG trap set, until after the first prompt is displayed.

bash_it.sh

@@ -155,6 +155,3 @@ if ! _command_exists reload && [[ -n "${BASH_IT_RELOAD_LEGACY:-}" ]]; then
 			;;
 	esac
 fi
-
-# Disable trap DEBUG on subshells - https://github.com/Bash-it/bash-it/pull/1040
-set +T