Speed up kernel CI: ccache depend mode, drop pahole deps, no module compression

- ccache: enable depend mode (skip the preprocessor on ~75k compiler
  calls) and add BASEDIR/NOHASHDIR/SLOPPINESS as insurance against false
  misses from build-path or build-macro churn. ccache -s already shows
  99.99% direct hits, so this trims per-call overhead, not a broken
  cache. MAXSIZE stays 8G (only ~1G used).
- deps: drop dwarves + libdw-dev. pahole only runs with
  CONFIG_DEBUG_INFO_BTF, but the build forces DEBUG_INFO_NONE, so they
  were never used.
- config: disable MODULE_COMPRESS/MODULE_DECOMPRESS for both arches.
  arm64 alone shipped zstd module compression, running a zstd pass over
  ~8000 .ko every build for no gain (the .deb is already compressed by
  KDEB_COMPRESS); x86_64 never did. Keeps the two arches in sync.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

scripts/prepare-kernel-config.sh

@@ -68,6 +68,16 @@ apply_policy_config() {
   scripts/config --disable INET6_ESP
   scripts/config --disable AF_RXRPC
   scripts/config --disable RXKAD
+
+  # Don't compress modules at build time. arm64.config historically shipped
+  # CONFIG_MODULE_COMPRESS=y (zstd) while x86-64.config did not, so every arm64
+  # build ran a zstd pass over ~8000 .ko for no benefit: the published .deb is
+  # already compressed by KDEB_COMPRESS, and x86_64 proves the kernel ships fine
+  # with uncompressed on-disk modules. Disabling here keeps both arches in sync;
+  # olddefconfig drops the now-invisible MODULE_COMPRESS_* / MODULE_DECOMPRESS
+  # children. (Trade-off: installed /lib/modules .ko are uncompressed on disk.)
+  scripts/config --disable MODULE_COMPRESS
+  scripts/config --disable MODULE_DECOMPRESS
 }
 
 require_config_line() {