Duplicate test functions go undetected under --parallel #1147

Problem

A file defining the same test function twice is caught sequentially and ignored
entirely under --parallel — the mode CI runs.

function test_same() { assert_same 1 1; }
function test_same() { assert_same 2 2; }

$ bashunit --no-parallel dup_test.sh
Duplicate test functions found
Duplicate functions: test_same          # exit 1

$ bashunit --parallel dup_test.sh
✓ Passed: Same
 All tests passed                        # exit 0

This matters because bash silently discards the first definition: one of the two
tests never runs. The check exists precisely to catch that, and it is off in the
mode most projects use in CI.

Cause

check_duplicate_functions runs inside call_test_functions, which
load_test_files backgrounds per file under --parallel. The state it sets
dies with the subshell, exactly like the counter in #1145 — only .result
files cross that boundary.

Fix

Run the duplicate check in the parent, before the per-file dispatch, so it is
independent of the run mode.

Also

The report names no line numbers:

Duplicate functions: test_same

In a long test file that means hunting for the second definition by hand. The
awk pass already walks every line, so recording them costs nothing.