Add BitPacked embeddings for RAG retrieval

[svilupp]

• Updated options for Binary embeddings (refer to release v0.18 for motivation). Adds utility functions pack_bits and unpack_bits to move between binary and UInt64 representations of embeddings. RAGTools adds the corresponding BitPackedBatchEmbedder and BitPackedCosineSimilarity for fast retrieval on these Bool<->UInt64 embeddings (credit to domluna's tinyRAG).

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 98.11321% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 92.97%. Comparing base (27e4301) to head (2c69e2e).

Files	Patch %	Lines
src/Experimental/RAGTools/retrieval.jl	96.00%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #152 +/- ## ========================================== + Coverage 92.91% 92.97% +0.05% ========================================== Files 42 42 Lines 3262 3303 +41 ========================================== + Hits 3031 3071 +40 - Misses 231 232 +1 ```

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