make tests/run.sh posix-compliant by using \033[ rather than \e

seems like \e is only offered in bash
not in zsh (I'm using VSCode's integrated shell, running zsh, and all I see is

~/projects/yosys-slang/tests | chore/warn-for-wait-and-expect $ ./run.sh
./unit/async.ys... \e[32mOK\e[0m
.
.
.

afaik, ubuntu uses dash, and the first thing that comes up online is that dash also sees this problem of not having \e function like this

Author: CheeksTheGeek

tests/run.sh

@@ -3,20 +3,25 @@ YOSYS=yosys
 TESTSDIR="$(dirname "${BASH_SOURCE[0]}")"
 PLUGIN="$(realpath "$TESTSDIR/../build/slang.so")"
 code=0
+NOCOLOR='\033[0m'
+RED='\033[0;31m'
+GREEN='\033[0;32m'
+BOLD='\033[1m'
+
 for testcase in "$TESTSDIR"/*/*.ys "$TESTSDIR"/*/*.tcl;
 do
 	TEXT=$testcase;
 	base=$(basename "$testcase")
 	dir=$(dirname "$testcase")
 	echo -n "${TEXT}... ";
-	if ! (cd "$dir" && exec "$YOSYS" -m "$PLUGIN" "$base" 1>/dev/null 2>&1); then
-		echo -e "\e[31mFAIL\e[0m";
-		echo -e "Testcase \e[1m${testcase}\e[0m failed";
+	if ! (cd "$dir" && exec "$YOSYS" -m "$PLUGIN" "$base" >/dev/null 2>&1); then
+		echo -e "${RED}FAIL${NOCOLOR}";
+		echo -e "Testcase ${BOLD}${testcase}${NOCOLOR} failed";
 		(cd "$dir" && exec "$YOSYS" -g -Q -m "$PLUGIN" "$base");
 		echo;
 		code=1;
 	else
-		echo -e "\e[32mOK\e[0m";
+		echo -e "${GREEN}OK${NOCOLOR}";
 	fi
 done;
 exit $code