Use sparse checkout on CI to halve incremental test time

On CI runners, skip docs/ and tests/ directories when cloning
FastAPI (62% of 18K files). The fastapi/ package source remains
intact for all test assertions. Locally, full clone is preserved.

Author: DeusData

tests/test_incremental.c

@@ -202,11 +202,21 @@ static int incremental_setup(void) {
 
     snprintf(g_repodir, sizeof(g_repodir), "%s/fastapi", g_tmpdir);
 
-    char cmd[512];
-    snprintf(cmd, sizeof(cmd),
-             "git clone --depth=1 --branch 0.99.1 --quiet "
-             "https://github.com/fastapi/fastapi.git '%s' 2>&1",
-             g_repodir);
+    /* On CI, use sparse checkout to skip docs/ and tests/ (~62% of files).
+     * Cuts indexing time roughly in half on slow shared runners. */
+    char cmd[1024];
+    if (getenv("CI")) {
+        snprintf(cmd, sizeof(cmd),
+                 "git clone --depth=1 --branch 0.99.1 --quiet --filter=blob:none "
+                 "--sparse https://github.com/fastapi/fastapi.git '%s' 2>&1 && "
+                 "cd '%s' && git sparse-checkout set --no-cone '/*' '!/docs' '!/tests' 2>&1",
+                 g_repodir, g_repodir);
+    } else {
+        snprintf(cmd, sizeof(cmd),
+                 "git clone --depth=1 --branch 0.99.1 --quiet "
+                 "https://github.com/fastapi/fastapi.git '%s' 2>&1",
+                 g_repodir);
+    }
     int rc = system(cmd);
     if (rc != 0) {
         printf("  clone failed (rc=%d) — network offline?\n", rc);