zsh: skip mkdir history directory when it exists

Every interactive shell ran `mkdir -p "$(dirname "$HISTFILE")"`, which
forks twice, even though the directory almost always exists. It costs
~10ms on macOS 27.

We now test if the directory exists first and use zsh's `:h` modifier
instead of dirname, so the most of the time no processes are started.
The directory is still created when missing.

modules/programs/zsh/history.nix

@@ -218,7 +218,7 @@ in
           cfg.history.ignorePatterns != [ ]
         ) "HISTORY_IGNORE=${lib.escapeShellArg "(${lib.concatStringsSep "|" cfg.history.ignorePatterns})"}"}
         HISTFILE="${mkShellVarPathStr cfg.history.path}"
-        mkdir -p "$(dirname "$HISTFILE")"
+        [[ -d ''${HISTFILE:h} ]] || mkdir -p "''${HISTFILE:h}"
       '')
 
       (lib.mkIf (cfg.historySubstringSearch.enable or false) (

tests/modules/programs/fabric-ai/zshrc

@@ -12,7 +12,7 @@ HISTSIZE="10000"
 SAVEHIST="10000"
 
 HISTFILE="/home/hm-user/.zsh_history"
-mkdir -p "$(dirname "$HISTFILE")"
+[[ -d ${HISTFILE:h} ]] || mkdir -p "${HISTFILE:h}"
 
 # Set shell options
 set_opts=(

tests/modules/programs/zsh/aliases.nix

@@ -29,7 +29,7 @@
       SAVEHIST="10000"
 
       HISTFILE="/home/hm-user/.zsh_history"
-      mkdir -p "$(dirname "$HISTFILE")"
+      [[ -d ''${HISTFILE:h} ]] || mkdir -p "''${HISTFILE:h}"
 
       # Set shell options
       set_opts=(

tests/modules/programs/zsh/history-substring-search-expected.zshrc

@@ -12,7 +12,7 @@ HISTSIZE="10000"
 SAVEHIST="10000"
 
 HISTFILE="/home/hm-user/.zsh_history"
-mkdir -p "$(dirname "$HISTFILE")"
+[[ -d ${HISTFILE:h} ]] || mkdir -p "${HISTFILE:h}"
 
 # Set shell options
 set_opts=(

tests/modules/programs/zsh/smart-formatting-expected.zshrc

@@ -12,7 +12,7 @@ HISTSIZE="50000"
 SAVEHIST="50000"
 
 HISTFILE="/home/hm-user/.zsh_history"
-mkdir -p "$(dirname "$HISTFILE")"
+[[ -d ${HISTFILE:h} ]] || mkdir -p "${HISTFILE:h}"
 
 # Set shell options
 set_opts=(

tests/modules/programs/zsh/zshrc-content-priorities.nix

@@ -69,7 +69,7 @@
           SAVEHIST="10000"
 
           HISTFILE="/home/hm-user/.zsh_history"
-          mkdir -p "$(dirname "$HISTFILE")"
+          [[ -d ''${HISTFILE:h} ]] || mkdir -p "''${HISTFILE:h}"
 
           # Set shell options
           set_opts=(