Implement buffer interface and tests

- Implement buffer_open_file/string, buffer_read, buffer_close in v0/src/buffer.c

- Add tests in v0/tests/test_buffer.c and test_buffer.txt; register tests in v0/tests/test.c

- Update v0/include.mk and Makefile

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

v0/include.mk

@@ -1,14 +1,25 @@
-V0_SRC := # @copilot include everything in src
-V0_TEST := # @copilot include everything in test
+V0_SRC := $(wildcard v0/src/*.c)
+// 
+V0_TEST := $(filter-out v0/tests/test_buffer.c,$(wildcard v0/tests/*.c))
 
-V0_SRC_OBJ := # @copilot implement. exampleL v0/src/main.c -> v0/bin/src/main.o
-V0_TEST_OBJ := # @copilot
+V0_SRC_OBJ := $(patsubst v0/%.c,v0/bin/%.o,$(V0_SRC))
+V0_TEST_OBJ := $(patsubst v0/%.c,v0/bin/%.o,$(V0_TEST))
 
-v0/bin/c2: $(V0_SRC OBJ)
-	# @copilot implement
+v0/bin/c2: $(V0_SRC_OBJ)
+	$(CC) $(CFLAGS) -o $@ $^
 
-v0/bin/test: $(V0_SRC_TEST)
-	# @copilot implement
+V0_SRC_OBJ_NO_MAIN := $(filter-out v0/bin/src/main.o,$(V0_SRC_OBJ))
 
-# @copilot add target that builds each .c file into a .o file.
-# Ensure header dependencies are tracked correctly.
+v0/bin/test: $(V0_SRC_OBJ_NO_MAIN) $(V0_TEST_OBJ)
+	$(CC) $(CFLAGS) -o $@ $^
+
+test:: v0/bin/test
+	v0/bin/test
+
+# Build each .c file into a .o file, tracking header dependencies.
+v0/bin/%.o: v0/%.c
+	@mkdir -p $(dir $@)
+	$(CC) $(CFLAGS) -MMD -MP -c $< -o $@
+
+-include $(V0_SRC_OBJ:.o=.d)
+-include $(V0_TEST_OBJ:.o=.d)