feat: Allow passing arbitrary Tensorizer serialization and deserialization kwargs; update docs

[sangstar]

Feature adding the following to the sangstar/tensorizer-aws-update-and-any-kwargs branch, which aims to add:

• Exposing arbitrary kwargs to Tensorizer from vLLM
• Harmonizing Tensorizer's AWS-style boto3 support with vLLM's
• Updating the docs to reflect these changes, greatly expanding upon the intended usage pattern so users can read it and immediately know how to get started

This is the kwargs-update portion. This PR adds:

• Exposing arbitrary kwargs to TensorSerializer and TensorDeserializer, adding tests to confirm functionality
• Update docs thoroughly to reflect straight-forward usage, including the new changes. The docs are not finished yet, as they'll be updated with the AWS-update feature to be included in the eventual PR for the aforementioned branch.

The changes herein are succinctly described in a snippet to the updated docs, describing how to load a model using Tensorizer with the updated arbitrary kwargs without too much pain in constructing the JSON string. The kwargs here are just throwaways demonstrating the support.

#!/bin/sh

MODEL_LOADER_EXTRA_CONFIG='{
  "tensorizer_uri": "s3://my-bucket/vllm/facebook/opt-125m/v1/model.tensors",
  "stream_kwargs": {"force_http": false},
  "deserialization_kwargs": {"verify_hash": true, "num_readers": 8}
}'

vllm serve facebook/opt-125m \
  --load-format=tensorizer \
  --model-loader-extra-config="$MODEL_LOADER_EXTRA_CONFIG"

Please hold off on any requests for changes relating to formatting. This will all be done in a later stage with vLLM's formatter.

[Eta0]

Please make sure that these three attributes are accounted for somewhere in self.deserializer_kwargs instead, even if they're deprecated.

[sangstar]

Like I did with the handling of the stream params, I'll bring this code snippet back and have it be overwritten by self.deserialization_kwargs if available, like:

        self.deserializer_params = {
            "verify_hash": self.verify_hash,
            "encryption": self.encryption_keyfile,
            "num_readers": self.num_readers
        }

        self.deserializer_params.update(**self.deserialization_kwargs)

[Eta0]

All good. Just update the PR description with the simplified shell script, please.