base recipe: make EXISTING_BINS filtering fast (one scan, not N full-tree greps)

The driver-list filter ran `grep -R "^name = \"$bin\"$" $COOKBOOK_SOURCE`
once PER bin (~40 bins). $COOKBOOK_SOURCE is local/sources/base, whose
target/ build tree is ~8.7 GB, so each grep re-scanned gigabytes and the
whole loop scanned hundreds of GB — a very slow build phase.

Collect the workspace's crate names ONCE from Cargo.toml files (skipping
target/ via --exclude-dir), into a bash associative array, then do an
O(1) membership check per bin. Verified equivalent (same bins selected)
and near-instant: the single scan of local/sources/base completes in
~0.02s vs minutes for the per-bin recursive greps.

recipes/core/base/recipe.toml

@@ -160,11 +160,21 @@ esac
 mkdir -pv "${COOKBOOK_STAGE}/usr/bin" "${COOKBOOK_STAGE}/usr/lib/drivers"
 export CARGO_PROFILE_RELEASE_OPT_LEVEL=s
 export CARGO_PROFILE_RELEASE_PANIC=abort
-# Only build drivers that actually have source Cargo.toml entries
+# Only build drivers that actually have source Cargo.toml entries.
+# Collect the workspace's crate names ONCE from Cargo.toml files, skipping the
+# multi-GB target/ build trees. The previous code ran a full recursive grep of
+# the entire source (including target/, ~8.7 GB) for EVERY bin (~40 of them),
+# re-scanning gigabytes per entry — extremely slow. One scan + O(1) membership
+# lookup is equivalent and near-instant.
+declare -A HAVE_CRATE=()
+while IFS= read -r crate_name
+do
+    HAVE_CRATE["${crate_name}"]=1
+done < <(grep -Rhs --include=Cargo.toml --exclude-dir=target '^name = ' "${COOKBOOK_SOURCE}" | sed -E 's/^name = "([^"]+)".*/\\1/')
 EXISTING_BINS=()
 for bin in "${BINS[@]}"
 do
-    if grep -Rqs "^name = \\\"${bin}\\\"$" "${COOKBOOK_SOURCE}"; then
+    if [[ -n "${HAVE_CRATE[${bin}]:-}" ]]; then
         EXISTING_BINS+=("${bin}")
     fi
 done