Memory-efficient zlib usage across Liberty file consumers

[widlarizer]

In ASIC flows, Liberty files provided in the PDK can be very large and are often compressed with gzip. Prior to this PR, the only pass that accepted .lib.gz was read_liberty, just like read_verilog accepts .v.gz etc. -liberty filename arguments to passes like clockgate and dfflibmap didn't use the decompression code.

The decompress_gzip function also has been reading the entirety of the uncompressed file into RAM (into a stringstream). This is now fixed by implementing an gzip_istream much like the pre-existing gzip_ostream. It has one byte of guaranteed unget() which is sufficient for our Liberty parsing. Using gzstream was ruled out because it's LGPL.

The PR carries also some shuffling of things around which should have limited impact on plugin devs since the new kernel/io.h header is included in kernel/yosys_common.h.

This will resolve #4830 but only on the Yosys side. The Yosys abc pass only hands off the paths specified with abc -liberty path to abc but abc doesn't support .lib.gz which is surprising since it does have its own vendored zlib and wrapper around it used for aiger

[povik]

I've only reviewed gzip.cc/gzip.h, it looks fine except for the nits

[povik]

Reading https://en.cppreference.com/w/cpp/io/basic_streambuf/underflow we might need to do something about "On failure, the function ensures that either gptr() == nullptr or gptr() == egptr." because the invariant of when this function is called is weaker, it is "The public functions of std::streambuf call this function only if gptr() == nullptr or gptr() >= egptr()."

[widlarizer]

Nice catch, now I setg(eback(), egptr(), egptr()); before returning eof