maint/CICD ~ implement 'GnuTests' workflow fixes/refactor

- consolidate configuration
- DRY improvements
- improve flexibility/robustness in the face of missing reference test info
- add reference test info IDs and additional logging to help diagnose testing failures
- includes parallel refactor of 'util/run-gnu-test.sh'

util/run-gnu-test.sh

@@ -1,10 +1,28 @@
 #!/bin/bash
+# `$0 [TEST]`
+# run GNU test (or all tests if TEST is missing/null)
 # spell-checker:ignore (env/vars) BUILDDIR GNULIB SUBDIRS
-cd "$(dirname -- "$(readlink -fm -- "$0")")/../.."
+
+ME_dir="$(dirname -- "$(readlink -fm -- "$0")")"
+REPO_main_dir="$(dirname -- "${ME_dir}")"
+
 set -e
-BUILDDIR="${PWD}/uutils/target/release"
-GNULIB_DIR="${PWD}/gnulib"
-pushd gnu
+
+### * config (from environment with fallback defaults)
+
+path_UUTILS=${path_UUTILS:-${REPO_main_dir}}
+path_GNU=${path_GNU:-${path_UUTILS}/../gnu}
+path_GNULIB=${path_GNULIB:-${path_UUTILS}/../gnulib}
+
+###
+
+BUILD_DIR="$(realpath -- "${path_UUTILS}/target/release")"
+GNULIB_DIR="$(realpath -- "${path_GNULIB}")"
+
+export BUILD_DIR
+export GNULIB_DIR
+
+pushd "$(realpath -- "${path_GNU}")"
 
 export RUST_BACKTRACE=1