[nanvix] E: Build bz2/lzma/zlib/sqlite3 as DT_NEEDED .so chains

[esaurez]

Summary

Completes the external-library unbundling started in nanvix/cpython#738 by moving the remaining four stdlib extensions (_bz2, _lzma, zlib, _sqlite3) from being statically linked into python.elf to runtime-loaded .so files emitting DT_NEEDED for libbz2.so / liblzma.so / libz.so / libsqlite3.so.

After this PR, python.elf bundles no external Nanvix-ported libraries at all — every .so wrapper (_ssl, _hashlib, _ctypes, _sqlite3, zlib, _bz2, _lzma) consumes its underlying library through DT_NEEDED. This matches upstream cpython's default behavior on every Linux distro (system-library detection enabled).

Why

The previous PR (nanvix/cpython#738) took the libffi / openssl / lxml consumers to DT_NEEDED .so chains but left these four extensions statically linked into python.elf because the Nanvix port repos for bzip2 / zlib / xz / sqlite did not yet ship .so builds. The four port-repo PRs listed under Dependencies below add those .so builds, which finally lets this PR finish the migration.

What changed

4 stdlib modules migrated from *static* (linked into python.elf) to *shared* (loaded via dlopen). The corresponding LIBSQLITE3_LIBS / ZLIB_LIBS / BZIP2_LIBS / LIBLZMA_LIBS env vars already use -L/-l form in nanvix/cpython#738 (no change needed there); cpython's normal MODULE_*_LDFLAGS machinery wires them into each .so's link line as DT_NEEDED.

DT_NEEDED .so chains added by this PR:
  _bz2.cpython-312.so       -> libbz2.so
  _lzma.cpython-312.so      -> liblzma.so
  zlib.cpython-312.so       -> libz.so
  _sqlite3.cpython-312.so   -> libsqlite3.so

The Nanvix dynamic loader walks each DT_NEEDED chain at dlopen() time, and UND symbols in any of those .so files bind to python.elf .dynsym.

Mechanics

File	Change
.nanvix/setup_local.py	Adds 4 *shared* entries (_bz2, _lzma, zlib, _sqlite3).
Makefile.nanvix	Drops -lsqlite3 -lz -lbz2 -llzma from python.elf LIBS; the -Wl,--start-group ... -Wl,--end-group block is gone. Per-module *_LIBS env vars unchanged (already in -L/-l form from nanvix/cpython#738).
.nanvix/runtime_sos.py	REQUIRED_RUNTIME_SOS gains libbz2.so / liblzma.so / libz.so / libsqlite3.so so .nanvix/test.py and .nanvix/package.py stage them into sysroot/lib/ at run time.
.nanvix/z.py	_DEP_EXPECTED_LIBS for bzip2, zlib, sqlite, xz extended with the .so siblings so ./z setup validates that the new shared-library port builds installed correctly into buildroot/lib.
.nanvix/test.py	Extends CPYTHON_TEST_EXTERNAL_DEPS smoke test with the 4 new modules.

Dependencies

Base branch: nanvix/cpython#738.

Runtime dependencies — the four port-repo PRs that produce the .so files this PR consumes:

• nanvix/bzip2#279 — libbz2.so build target.
• nanvix/zlib#255 — libz.so build target.
• nanvix/xz#97 — liblzma.so build target.
• nanvix/sqlite#268 — libsqlite3.so build target.

These four PRs must land and their port-lib releases must be pinned in cpython's nanvix.toml before this PR is mergeable upstream.

Also inherits the runtime deps already required by nanvix/cpython#738:

• nanvix/nanvix#2473 — dlfcn init-array + DT_RUNPATH support (already merged upstream).
• The upstream diamond DT_NEEDED loader fix and the libposix pthread_once fix described in [nanvix] E: Build _ssl/_hashlib/_ctypes as .so nanvix/cpython#738 (in-flight in nanvix/nanvix).

Co-authored-by: Copilot 223556219+Copilot@users.noreply.github.com