fix(shell): fix incorrect timing of child shells (#1510)

When a child shell session is started from another shell session
(parent session), the environment variable ATUIN_HISTORY_ID set by the
parent session causes Atuin's precmd hook of the child session to be
unexpectedly performed before the first call of Atuin's preexec hook.

In this patch, we clear ATUIN_HISTORY_ID (possibly set by the parent
session) on the startup of the session.

atuin/src/shell/atuin.bash

@@ -1,6 +1,7 @@
 ATUIN_SESSION=$(atuin uuid)
 ATUIN_STTY=$(stty -g)
 export ATUIN_SESSION
+ATUIN_HISTORY_ID=""
 
 __atuin_preexec() {
     if [[ ! ${BLE_ATTACHED-} ]]; then

atuin/src/shell/atuin.fish

@@ -1,4 +1,5 @@
 set -gx ATUIN_SESSION (atuin uuid)
+set --erase ATUIN_HISTORY_ID
 
 function _atuin_preexec --on-event fish_preexec
     if not test -n "$fish_private_mode"

atuin/src/shell/atuin.nu

@@ -1,5 +1,6 @@
 # Source this in your ~/.config/nushell/config.nu
 $env.ATUIN_SESSION = (atuin uuid)
+hide-env -i ATUIN_HISTORY_ID
 
 # Magic token to make sure we don't record commands run by keybindings
 let ATUIN_KEYBINDING_TOKEN = $"# (random uuid)"

atuin/src/shell/atuin.zsh

@@ -25,6 +25,7 @@ else
 fi
 
 export ATUIN_SESSION=$(atuin uuid)
+ATUIN_HISTORY_ID=""
 
 _atuin_preexec() {
     local id