feat: add minimal path manipulation C module for internal VM use

Introduce a new `Path` struct and associated functions in `src/cli/path.c` and `src/cli/path.h` for resolving relative imports within the VM. The module provides operations such as normalization, directory extraction, extension removal, joining, and absolute path detection. Additionally, add a lightweight unit test framework under `test/unit/` with a `test.h`/`test.c` harness and `path_test.c` covering normalization cases. Update the build system (`Makefile`, `util/wren.mk`) to separate API tests from unit tests, rename the test executables to `api_wren` and `unit_wren`, and adjust CI targets and Python test scripts accordingly.

test/unit/main.c

@@ -0,0 +1,9 @@
+#include "path_test.h"
+#include "test.h"
+
+int main()
+{
+  testPath();
+  
+  return showTestResults();
+}

test/unit/path_test.c

@@ -0,0 +1,105 @@
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "path.h"
+#include "test.h"
+
+static void expectNormalize(const char* input, const char* expected)
+{
+  Path* path = pathNew(input);
+  Path* result = pathNormalize(path);
+  
+  if (strcmp(result->chars, expected) != 0)
+  {
+    printf("FAIL %-30s Want %s\n", input, expected);
+    printf("                                     Got %s\n\n", result->chars);
+    fail();
+  }
+  else
+  {
+#if SHOW_PASSES
+    printf("PASS %-30s   -> %s\n", input, result->chars);
+#endif
+    pass();
+  }
+  
+  pathFree(path);
+  pathFree(result);
+}
+
+static void testNormalize()
+{
+  // simple cases
+  expectNormalize("", ".");
+  expectNormalize(".", ".");
+  expectNormalize("..", "..");
+  expectNormalize("a", "a");
+  expectNormalize("/", "/");
+  
+  // collapses redundant separators
+  expectNormalize("a/b/c", "a/b/c");
+  expectNormalize("a//b///c////d", "a/b/c/d");
+  
+  // eliminates "." parts
+  expectNormalize("./", ".");
+  expectNormalize("/.", "/");
+  expectNormalize("/./", "/");
+  expectNormalize("./.", ".");
+  expectNormalize("a/./b", "a/b");
+  expectNormalize("a/.b/c", "a/.b/c");
+  expectNormalize("a/././b/./c", "a/b/c");
+  expectNormalize("././a", "a");
+  expectNormalize("a/./.", "a");
+  
+  // eliminates ".." parts
+  expectNormalize("..", "..");
+  expectNormalize("../", "..");
+  expectNormalize("../../..", "../../..");
+  expectNormalize("../../../", "../../..");
+  expectNormalize("/..", "/");
+  expectNormalize("/../../..", "/");
+  expectNormalize("/../../../a", "/a");
+  expectNormalize("a/..", ".");
+  expectNormalize("a/b/..", "a");
+  expectNormalize("a/../b", "b");
+  expectNormalize("a/./../b", "b");
+  expectNormalize("a/b/c/../../d/e/..", "a/d");
+  expectNormalize("a/b/../../../../c", "../../c");
+  
+  // does not walk before root on absolute paths
+  expectNormalize("..", "..");
+  expectNormalize("../", "..");
+  expectNormalize("/..", "/");
+  expectNormalize("a/..", ".");
+  expectNormalize("../a", "../a");
+  expectNormalize("/../a", "/a");
+  expectNormalize("/../a", "/a");
+  expectNormalize("a/b/..", "a");
+  expectNormalize("../a/b/..", "../a");
+  expectNormalize("a/../b", "b");
+  expectNormalize("a/./../b", "b");
+  expectNormalize("a/b/c/../../d/e/..", "a/d");
+  expectNormalize("a/b/../../../../c", "../../c");
+  expectNormalize("a/b/c/../../..d/./.e/f././", "a/..d/.e/f.");
+  
+  // removes trailing separators
+  expectNormalize("./", ".");
+  expectNormalize(".//", ".");
+  expectNormalize("a/", "a");
+  expectNormalize("a/b/", "a/b");
+  expectNormalize("a/b///", "a/b");
+  
+  expectNormalize("foo/bar/baz", "foo/bar/baz");
+  expectNormalize("foo", "foo");
+  expectNormalize("foo/bar/", "foo/bar");
+  expectNormalize("./foo/././bar/././", "foo/bar");
+}
+
+void testPath()
+{
+  // TODO: Test other functions.
+  testNormalize();
+}
+

test/unit/path_test.h

@@ -0,0 +1 @@
+void testPath();

test/unit/test.c

@@ -0,0 +1,29 @@
+#include <stdio.h>
+
+#include "test.h"
+
+int passes = 0;
+int failures = 0;
+
+void pass()
+{
+  passes++;
+}
+
+void fail()
+{
+  failures++;
+}
+
+int showTestResults()
+{
+  if (failures > 0)
+  {
+    printf("%d out of %d tests failed. :(\n", failures, passes + failures);
+    return 1;
+  }
+  
+  printf("All %d tests passed!\n", passes + failures);
+  return 0;
+}
+

test/unit/test.h

@@ -0,0 +1,7 @@
+// Set this to 1 to output passing tests.
+#define SHOW_PASSES 0
+
+void pass();
+void fail();
+
+int showTestResults();