build: Compress the RPM payload with zstd (#8047)

.cspell.config.yaml

@@ -384,4 +384,5 @@ words:
   - xrplf
   - xxhash
   - xxhasher
+  - zstdio
   - CGNAT

package/README.md

@@ -238,14 +238,9 @@ what catches a binary still linked against the Nix store's ELF loader (see
 3. Runs `rpmbuild -bb`, passing the normalized package metadata version as the
    `pkg_version` RPM macro and `PKG_RELEASE` as the `pkg_release` RPM macro.
    The spec uses manual `install` commands to place files, disables `dwz`, and
-   writes uncompressed RPM payloads while generating debuginfo packages.
+   generates debuginfo packages.
 4. Output: `rpmbuild/RPMS/x86_64/xrpld-*.rpm`
 
-The uncompressed RPM payload setting is intentionally unconditional for
-generated RPMs. It trades larger RPM artifacts for much shorter package
-build/validation time, which keeps RPM package validation in the same rough time
-class as Debian package validation.
-
 RPM upgrades intentionally do not restart a running `xrpld` service. The spec
 uses `%systemd_postun`, matching Debian's `dh_installsystemd
 --no-stop-on-upgrade` behavior; operators pick up the new binary on the next

package/rpm/xrpld.spec

@@ -19,8 +19,10 @@ BuildRequires: systemd-rpm-macros
 
 %undefine _debugsource_packages
 %debug_package
-# Intentionally trade larger RPM artifacts for faster package validation.
-%global _binary_payload w.ufdio
+# Level 3 rather than the el9 default of 19: it shrinks the multi-gigabyte
+# debuginfo package roughly fourfold in about a second, where 19 would spend
+# minutes on it.
+%global _binary_payload w3.zstdio
 %global _find_debuginfo_dwz_opts %{nil}
 
 %build_mtime_policy clamp_to_source_date_epoch