chore: Migrate tests to cmp package

[SuperQ]

Migrate the majority of diff tests from reflect.DeepEqual() to cmp.Diff() to improve the test failure readability.

[SuperQ]

Tool assisted speedrun:

#!/usr/bin/env bash
#
# Description: Convert refelect tests to cmp.
#

if [[ $# -ne 1 ]]; then
  echo "usage: $(basename $0) <file>"
  exit 1
fi

file="$1"

if [[ ! -f "${file}" ]] ; then
  echo "ERROR: ${file} not found"
  exit 1
fi

sed_script="$(cat << 'SEDSCRIPT'
s/if !reflect.DeepEqual\((.+), (.+)\) \{/if diff := cmp.Diff(\1, \2); diff != "" {\nt.Fatalf("unexpected diff (-want +got):\\n\%s", diff)/
SEDSCRIPT
)"

sed -i -E "${sed_script}" "${file}"

goimports -w "${file}"

go fmt "${file}"