modules/zstd: Add support for decoding compressed blocks

[lpawelcz]

This PR extends the ZstdDecoder with support for decoding compressed blocks.

It supersedes PRs:

• modules/zstd: Add sequence decoding #1362
• modules/zstd: Add literals decoding #1430
• Add cocotb tests for AXI peripherals #1616
• modules/zstd: Rework ZSTD Decoder #1654

The decoder is capable of decoding RAW and RLE literals as well as sequences with predefined FSE tables.
A suite of DSLX tests comprising unit tests of all underlying procs and an integration test was prepared.
The integration test, similarly as in #1654, first generates a random valid ZSTD frame with compressed blocks and expected decoded output. Test data is then converted to a DSLX file (example) that is imported by the integration tests file.
At the beginning of the test, the default FSE decoding tables are filled with default distributions taken from RFC 8878 section 3.1.1.3.2.2. Default Distributions . Next, the encoded frame is loaded to the system memory and the decoder is configured through a set of CSRs to start the decoding process. The decoder starts the operation and writes the decoded frame back into the output buffer in the system memory. Once it finishes, it sends a pulse on the notify channel signaling the end of the decoding. The output of the decoder is compared against the decoding result from the reference library.

The PR introduces among others:

• CompressedBlockDecoder - manages both SequenceDecoder and LiteralsDecoder to enable compress block decoding. Integrated with the top-level ZstdDecoder
• SequenceDecoder - responsible for decoding sequence sections of the compressed blocks
• FseDecoder - introduced as the core part of the SequenceDecoder
• RefillingShiftBuffer - used for storing and outputting in forward and backward fashion an arbitrary amount of bits required by the FSE decoder
• LiteralsDecoder - capable of decoding RAW, RLE and Huffman-coded literals
• HuffmanDecoder - used in decoding huffman-coded literals. Decoded Huffman trees are then used to decode one or four Huffman-coded streams.
• CommandConstructor - this proc is responsible for sending packets with decoded sequences and literals to the SequenceExecutor proc
• RamMux and RamDemux - procs used for handling requests/responses to multiple memory models. The procs interface with 3 separate memory buffers for FSE decoding tables.

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[proppy]

Can we rebase and consolidate with #1654 ?

[lpawelcz]

Can we rebase and consolidate with #1654 ?

@proppy done
This PR also supersedes #1616 so I also closed it in favor of this one