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

tools/autoconf.bzl

@@ -1,6 +1,6 @@
 "Utilities for replicating autoconf behavior"
 
-load("@aspect_bazel_lib//lib:expand_template.bzl", "expand_template")
+load("@bazel_lib//lib:expand_template.bzl", "expand_template")
 
 def define_macro_if(macro, condition):
     """Controls conditional macro definition based on a build condition.

tools/transition.bzl

@@ -1,6 +1,6 @@
 "Transition build and platform settings"
 
-load("@rules_cc//cc:defs.bzl", "CcInfo")
+load("@rules_cc//cc/common:cc_info.bzl", "CcInfo")
 
 PLATFORM = select({
     "@platforms//os:freebsd": "freebsd",