The default lancedb wheel targets target-cpu=haswell (AVX2 + FMA + F16C)
and SIGILLs at import on pre-Haswell silicon (Sandy Bridge / Ivy Bridge /
Westmere on Intel; Bulldozer / Piledriver / Steamroller on AMD). Per
westonpace's review on lancedb#3324 (fast by default, extra steps to work on
legacy), the default wheel baseline stays fast for modern users;
pre-Haswell users get a separately-published 'lancedb-compat' wheel.

Adds a 'lancedb-compat' matrix entry to pypi-publish.yml that builds
with RUSTFLAGS=-C target-cpu=x86-64-v2 (Nehalem-class baseline). The
compat wheel relies on runtime SIMD dispatch in the embedded lance crate
(landing via lance-format/lance#6630) to pick the appropriate kernel
tier at load time, so it still goes fast on modern hardware.

Generalizes build_linux_wheel and upload_wheel composites with optional
package-name and rustflags inputs (defaults preserve current behavior
for the existing 4 lancedb matrix entries). Documents the choice in
python/README.md: pip install lancedb-compat for pre-Haswell hosts;
same import lancedb API.

Maintainer setup required before this can ship: register lancedb-compat
on PyPI and configure trusted publishing.

Blocked on lance-format/lance#6630.

…re-haswell-build

# Conflicts:
#	.github/workflows/build_linux_wheel/action.yml

The compat wheel targeted manylinux 2_17, which lancedb no longer
supports. The variant exists to support outdated hardware, not outdated
glibc, so it now builds on 2_28 like the other wheels.

Since all three linux matrix entries are now x86_64/aarch64 on 2_28, the
job name and wheel artifact name no longer uniquely identify an entry.
Both now include the package name.

Also widen the Fury upload glob, which matched lancedb-*.whl and so
would have skipped the compat wheel -- its distribution filename
normalizes to lancedb_compat-*.whl.

The rustflags input was interpolated unconditionally into docker-options,
which broke both wheels.

For the default lancedb builds the input is empty, so the container got
'-e RUSTFLAGS='. Cargo treats RUSTFLAGS as an override whenever it is set --
even to the empty string -- so it discarded the per-target rustflags in
.cargo/config.toml and silently dropped -Ctarget-cpu=haswell and
+avx2,+fma,+f16c from the released x86_64 wheel. The same input default made
this true of the CI wheel built by python.yml.

For the compat build the value contained a space. maturin-action argv-splits
docker-options (string-argv), so '-e RUSTFLAGS=-C target-cpu=x86-64-v2' tore
into 'RUSTFLAGS=-C' plus a stray 'target-cpu=x86-64-v2' argument to docker run.

The '-e RUSTFLAGS=...' argument is now emitted only when the input is
non-empty, and the value is a single whitespace-free token.