compress: consolidate all compression into compress.c with dlopen

Move the push-based streaming compression API from import-compress.c
into compress.c and delete import-compress.c/h. This consolidates all
compression code in one place and makes all compression libraries
(liblzma, liblz4, libzstd, libz, libbz2) runtime-loaded via dlopen
instead of directly linked.

Introduce opaque Compressor/Decompressor types backed by a heap-
allocated struct defined only in compress.c, keeping all third-party
library headers out of compress.h.

Rewrite the per-codec fd-to-fd stream functions as thin wrappers around
the push API via generic compress_stream()/decompress_stream() taking a
Compression type parameter. Integrate LZ4 into this framework using the
LZ4 Frame API, eliminating all LZ4 special-casing.

Extend the Compression enum with COMPRESSION_GZIP and COMPRESSION_BZIP2
and add the corresponding blob, startswith, and stream functions for
both.

Rename the ImportCompress types and functions: ImportCompressType becomes
the existing Compression enum, ImportCompress becomes Compressor (with
Decompressor typedef), and all import_compress_*/import_uncompress_*
become compressor_*/decompressor_*. Rename dlopen_lzma() to dlopen_xz()
for consistency. Make compression_to_string() return lowercase by
default.

Add INT_MAX/UINT_MAX overflow checks for LZ4, zlib, and bzip2 blob
functions where the codec API uses narrower integer types than our
uint64_t parameters.

Migrate test-compress.c and test-compress-benchmark.c to the TEST()
macro framework, new assertion macros, and codec-generic loops instead
of per-codec duplication.

Co-developed-by: Claude Opus 4.6 <noreply@anthropic.com>

src/basic/meson.build

@@ -211,12 +211,14 @@ libbasic_static = static_library(
         fundamental_sources,
         include_directories : basic_includes,
         implicit_include_directories : false,
-        dependencies : [libdl,
+        dependencies : [libbzip2_cflags,
+                        libdl,
                         libgcrypt_cflags,
                         liblz4_cflags,
                         libm,
                         librt,
                         libxz_cflags,
+                        libz_cflags,
                         libzstd_cflags,
                         threads,
                         userspace],