[BUILD] Restore Debian/RPM packaging lost in history rewrite; add openEuler 24.03 RPM support

[shiptux]

Summary

Restores the Debian/RPM packaging merged in #607 — the merge commit
(e56773e1) is no longer an ancestor of main after the branch
history was rewritten, so all packaging files vanished from the tree
— and extends it with openEuler 24.03 LTS RPM support (part of
the FlagOS-on-openEuler effort; same pattern as
flagos-ai/FlagSparse#29 and flagos-ai/FlagAttention#35, both green).

What changed

Recovered from the #607 merge commit (unchanged):
packaging/{debian,rpm,INSTALL.md,README.md,spike},
.github/workflows/build-{deb,rpm}.yml, .dockerignore.

Re-ported to the post-rewrite tree:

• setup.py / pyproject.toml / MANIFEST.in moved to the repo
  root — wheel-builder COPY lists and build WORKDIR updated in both
  Dockerfiles. The narrow COPY is kept on purpose: packaging-only
  edits must not invalidate the ~50 min wheel layer.
• The new tileir default backend requires GCC >= 13 and the
  cuda-tile submodule; distro toolchains can't satisfy that
  (openEuler 24.03 ships GCC 12.3). Added a
  FLAGTREE_DEFAULT_BACKENDS env knob in
  python/setup_tools/utils/tools.py (one field change, default
  unchanged: nvidia,amd,tileir); packaging builds pin
  FLAGTREE_DEFAULT_BACKENDS=nvidia,amd — the same contents the
  historical wheel/packages shipped.

openEuler 24.03 additions:

• build-flagtree-rpm.sh: RPM_BASE_IMAGE env passthrough
  (default fedora:43 unchanged).
• build-rpm.yml: fedora43 + openeuler2403 matrix
  (fail-fast: false); the Fedora artifact keeps its exact name
  (flagtree-nvidia-rpm-packages), openEuler uploads as
  flagtree-nvidia-oe2403-rpm-packages.
• Dockerfile.rpm: reconstructs the empty %dist on openEuler
  images (.oe2403).
• flagtree.spec: %%-escaped macros in preamble comments —
  openEuler's rpm expands macros inside comments, and the bare
  %install in the usage note terminated the preamble
  ("Version field must be present" errors).

Tested

Both matrix targets built locally end-to-end:

Target	Artifact	Python ABI	Result
fedora43	python3-flagtree-nvidia-0.5.0-1.fc43.x86_64.rpm	cp314	wheel + rpm build pass
openeuler2403	python3-flagtree-nvidia-0.5.0-1.oe2403.x86_64.rpm	cp311	installs on openeuler/openeuler:24.03-lts; import triton OK (3.6.0)

The openEuler cp311 package is the missing piece that unblocks
dnf install python3-flagtree-nvidia on openEuler 24.03 (the
previously published cp310 build is Python-ABI-locked).

Limitations

• nvidia backend only, as in [BUILD] Add Debian + RPM packaging for the nvidia backend #607.
• build-deb.yml restored as-is (ubuntu22.04/cp310); openEuler
  affects the RPM side only.
• The wheel layer downloads LLVM/NVIDIA toolchains at build time;
  transient download failures fail the job (retry).

[zhzhcookie]

LGTM