Add unit tests for FileCollector, CommandBase filters, and StatsAnalyser

- test_file_collector.cpp: 11 tests for file/directory collection
- test_command_base.cpp: 28 tests for filtering logic (date, value, errors)
- test_stats_analyser.cpp: 32 tests for statistical functions (isNumeric,
  median, stddev, percentile)
- Fix test_error_detector.cpp Windows compatibility (mkdir/rmdir)
- Update Makefile with all new unit test targets

Author: edwbaker

Makefile

@@ -19,11 +19,11 @@ endif
 # Source files
 SOURCES = src/sensor-data.cpp
 LIB_SOURCES = src/csv_parser.cpp src/json_parser.cpp src/error_detector.cpp src/file_utils.cpp src/sensor_data_transformer.cpp src/data_counter.cpp src/error_lister.cpp src/error_summarizer.cpp src/stats_analyser.cpp src/latest_finder.cpp
-TEST_SOURCES = tests/test_csv_parser.cpp tests/test_json_parser.cpp tests/test_error_detector.cpp tests/test_file_utils.cpp tests/test_date_utils.cpp tests/test_common_arg_parser.cpp tests/test_data_reader.cpp
+TEST_SOURCES = tests/test_csv_parser.cpp tests/test_json_parser.cpp tests/test_error_detector.cpp tests/test_file_utils.cpp tests/test_date_utils.cpp tests/test_common_arg_parser.cpp tests/test_data_reader.cpp tests/test_file_collector.cpp tests/test_command_base.cpp tests/test_stats_analyser.cpp
 
 # Object files
 LIB_OBJECTS = $(LIB_SOURCES:.cpp=.o)
-TEST_EXECUTABLES = test_csv_parser test_json_parser test_error_detector test_file_utils test_date_utils test_common_arg_parser test_data_reader
+TEST_EXECUTABLES = test_csv_parser test_json_parser test_error_detector test_file_utils test_date_utils test_common_arg_parser test_data_reader test_file_collector test_command_base test_stats_analyser
 
 TARGET = sensor-data
 
@@ -47,6 +47,9 @@ test: $(LIB_OBJECTS)
 	@$(CXX) $(CPPFLAGS) $(CXXFLAGS) tests/test_date_utils.cpp -o test_date_utils $(LDFLAGS) && ./test_date_utils
 	@$(CXX) $(CPPFLAGS) $(CXXFLAGS) tests/test_common_arg_parser.cpp src/file_utils.o -o test_common_arg_parser $(LDFLAGS) && ./test_common_arg_parser
 	@$(CXX) $(CPPFLAGS) $(CXXFLAGS) tests/test_data_reader.cpp src/csv_parser.o src/json_parser.o src/file_utils.o -o test_data_reader $(LDFLAGS) && ./test_data_reader
+	@$(CXX) $(CPPFLAGS) $(CXXFLAGS) tests/test_file_collector.cpp src/file_utils.o -o test_file_collector $(LDFLAGS) && ./test_file_collector
+	@$(CXX) $(CPPFLAGS) $(CXXFLAGS) tests/test_command_base.cpp src/error_detector.o -o test_command_base $(LDFLAGS) && ./test_command_base
+	@$(CXX) $(CPPFLAGS) $(CXXFLAGS) tests/test_stats_analyser.cpp -o test_stats_analyser $(LDFLAGS) && ./test_stats_analyser
 	@echo "All unit tests passed!"
 
 # Run integration tests (requires bash)