p10k: improve jj prompt latency

prompt_my_jj is run on every command and so affects command_lag_ms, 
whereas _my_jj_async runs in the background and doesn't, so it needs to
be fast.

this change removes the jj workspace root call which takes about 10ms

Author: tekumara

README.md

@@ -26,9 +26,9 @@ has_compsys=1
 has_syntax_highlighting=1
 has_autosuggestions=1
 has_git_prompt=1
-first_prompt_lag_ms=80.679
-first_command_lag_ms=557.900
-command_lag_ms=41.683
-input_lag_ms=6.921
-exit_time_ms=371.420
+first_prompt_lag_ms=89.379
+first_command_lag_ms=535.799
+command_lag_ms=28.222
+input_lag_ms=7.376
+exit_time_ms=357.432
 ```

dotfiles/.p10k.zsh

@@ -1621,7 +1621,9 @@
     local workspace
 
     command -v jj >/dev/null 2>&1 || return
-    if workspace=$(jj workspace root 2>/dev/null); then
+
+    # check if we are in a jj repo
+    if [[ -n ./(../)#(.jj)(#qN/) ]]; then
       p10k display "*/jj=show"
       p10k display "*/vcs=hide"
     else
@@ -1630,6 +1632,8 @@
       return
     fi
 
+    workspace=$PWD
+
     # track current workspace for the async worker
     if [[ $_my_jj_workspace != "$workspace" ]]; then
       _my_jj_display=""