CI: Make download tool detection lazy

The download tool check was failing scripts that source common.sh but
don't use download functions (like riscv-tests.sh). This changes to lazy
initialization - only check for curl/wget when a download function is
actually called.

This prevents unnecessary failures in scripts that source common.sh
for other utilities like PARALLEL or check_platform().

Author: jserv

.ci/common.sh

@@ -24,20 +24,28 @@ fi
 # Universal download utility with curl/wget compatibility
 # Provides consistent interface regardless of which tool is available
 
-# Detect available download tool
-if command -v curl > /dev/null 2>&1; then
-    DOWNLOAD_TOOL="curl"
-elif command -v wget > /dev/null 2>&1; then
-    DOWNLOAD_TOOL="wget"
-else
-    echo "Error: Neither curl nor wget is available" >&2
-    exit 1
-fi
+# Detect available download tool (lazy initialization)
+detect_download_tool()
+{
+    if [ -n "${DOWNLOAD_TOOL:-}" ]; then
+        return 0
+    fi
+
+    if command -v curl > /dev/null 2>&1; then
+        DOWNLOAD_TOOL="curl"
+    elif command -v wget > /dev/null 2>&1; then
+        DOWNLOAD_TOOL="wget"
+    else
+        echo "Error: Neither curl nor wget is available" >&2
+        return 1
+    fi
+}
 
 # Download to stdout
 # Usage: download_to_stdout <url>
 download_to_stdout()
 {
+    detect_download_tool || return 1
     local url="$1"
     case "$DOWNLOAD_TOOL" in
         curl)
@@ -53,6 +61,7 @@ download_to_stdout()
 # Usage: download_to_file <url> <output_file>
 download_to_file()
 {
+    detect_download_tool || return 1
     local url="$1"
     local output="$2"
     case "$DOWNLOAD_TOOL" in
@@ -69,6 +78,7 @@ download_to_file()
 # Usage: download_with_headers <url> <header1> <header2> ...
 download_with_headers()
 {
+    detect_download_tool || return 1
     local url="$1"
     shift
     local headers=()
@@ -93,6 +103,7 @@ download_with_headers()
 # Usage: download_silent <url>
 download_silent()
 {
+    detect_download_tool || return 1
     local url="$1"
     case "$DOWNLOAD_TOOL" in
         curl)
@@ -108,6 +119,7 @@ download_silent()
 # Usage: download_with_progress <url> <output_file>
 download_with_progress()
 {
+    detect_download_tool || return 1
     local url="$1"
     local output="$2"
     case "$DOWNLOAD_TOOL" in
@@ -125,6 +137,7 @@ download_with_progress()
 # Returns: 0 if accessible, 1 otherwise
 check_url()
 {
+    detect_download_tool || return 1
     local url="$1"
     case "$DOWNLOAD_TOOL" in
         curl)