Cache lspci output in get_storage_controllers

The lspci command is now called only once on first invocation of
get_storage_controllers, with results cached in LSPCI_CACHE.

Subsequent calls from different layout generators (10bay, large1,
micro) reuse the cached output, reducing subprocess overhead.

Also added function documentation.

Fixes: #17

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

driveAtlas.sh

@@ -520,12 +520,29 @@ declare -A CHASSIS_TYPES=(
 # Core Functions
 #------------------------------------------------------------------------------
 
+# Cache for lspci output (populated on first call)
+LSPCI_CACHE=""
+
+#------------------------------------------------------------------------------
+# get_storage_controllers
+#
+# Returns a formatted list of storage controllers found via lspci.
+# Uses cached output if available to avoid redundant lspci calls.
+#
+# Output Format: "    PCI_ADDR: DESCRIPTION" (one per line)
+#------------------------------------------------------------------------------
 get_storage_controllers() {
-    # Returns a formatted list of storage controllers (HBAs, SATA, NVMe)
-    lspci 2>/dev/null | grep -iE "SAS|SATA|RAID|Mass storage|NVMe" | while read -r line; do
-        pci_addr=$(echo "$line" | awk '{print $1}')
+    # Cache lspci output on first call
+    if [[ -z "$LSPCI_CACHE" ]]; then
+        LSPCI_CACHE="$(lspci 2>/dev/null | grep -iE "SAS|SATA|RAID|Mass storage|NVMe")"
+    fi
+
+    # Format and return cached output
+    echo "$LSPCI_CACHE" | while read -r line; do
+        [[ -z "$line" ]] && continue
+        pci_addr="$(echo "$line" | awk '{print $1}')"
         # Get short description (strip PCI address)
-        desc=$(echo "$line" | sed 's/^[0-9a-f:.]\+ //')
+        desc="$(echo "$line" | sed 's/^[0-9a-f:.]\+ //')"
         echo "    $pci_addr: $desc"
     done
 }