fix(reports): use mktemp for parallel-safe HTML report temp file

The fixed filename temp_test_cases.txt caused race conditions when
running tests in parallel mode, leading to "No such file or directory"
errors when multiple subprocesses accessed the same file.

Author: Chemaclass

src/reports.sh

@@ -118,8 +118,9 @@ function bashunit::reports::generate_report_html() {
   local tests_failed=$(bashunit::state::get_tests_failed)
   local time=$(bashunit::clock::total_runtime_in_milliseconds)
 
-  # Temporary file to store test cases by file
-  local temp_file="temp_test_cases.txt"
+  # Temporary file to store test cases by file (use mktemp for parallel safety)
+  local temp_file
+  temp_file=$(mktemp "${TMPDIR:-/tmp}/bashunit-report.XXXXXX")
 
   # Collect test cases by file
   : >"$temp_file" # Clear temp file if it exists