perf: make pre-commit hooks pass file extensions

- shell-lint: faster evaluation of shell scripts, hook 40% faster;
- *-lint: unify method to find the "find" utility; and
- pre-commit: pass file extensions to lint tools.

scripts/markdown-lint.sh

@@ -7,19 +7,12 @@
 # shellcheck disable=SC2086
 set -eu
 
-command -v git >/dev/null ||
-  { printf "Missing program: git\n" >&2; exit 1; }
+command -v git >/dev/null || { echo "Missing program: git" >&2; exit 1; }
 cd "$(git rev-parse --show-toplevel)" || exit 1
 ./scripts/requires-program.sh mdl
 
 extra_files_rules="~MD002,~MD012,~MD022,~MD032,~MD041"
-
-find_tool="find"
-if command -v fd; then
-  find_tool="fd"
-elif command -v fdfind >/dev/null; then
-  find_tool="fdfind"
-fi
+find_tool="$(./scripts/best-program.sh fd fdfind find)"
 
 if test -n "${1-}"; then
   files=""