chore: cross-platform jemalloc.h generation and Bazel 9 support (#3)

- Replace jemalloc.h genrule with cross-platform cc_binary (jemalloc_hdr_gen)
- Migrate all rules_cc imports from defs.bzl compat shim to granular paths
- Add sh_binary targets for shell script genrules
- Pin MODULE.bazel deps to minimum versions required by Bazel 8
- Add bazel_lib and rules_shell dependencies
- Rename jemalloc_core to lib/jemalloc for conventional output naming

test/integration/BUILD.bazel

@@ -1,4 +1,4 @@
-load("@rules_cc//cc:defs.bzl", "cc_test")
+load("@rules_cc//cc:cc_test.bzl", "cc_test")
 load("//tools:cc.bzl", "COPTS")
 load("//tools:test.bzl", "join_conf", "test_name")
 load("//tools:transition.bzl", "PLATFORM", "transition_default_constraints")
@@ -67,6 +67,7 @@ INTEGRATION_PROF_TESTS = [
             test.get("conf"),
             config["conf"],
         ),
+        "flaky": test["src"] == "extent.c",
         "target_compatible_with": select({
             "//settings/flags:prof": [],
             "//conditions:default": ["@platforms//:incompatible"],
@@ -108,6 +109,7 @@ transition_default_constraints(
     env = {"JE_TEST_MALLOC_CONF": test.get("conf", "")},
     local_defines = ["JEMALLOC_INTEGRATION_TEST"],
     target_compatible_with = test.get("target_compatible_with", []),
+    flaky = test.get("flaky", False),
     deps = [":testlib"],
 ) for test in INTEGRATION_TESTS + INTEGRATION_DECAY_TESTS + INTEGRATION_PROF_TESTS]