A better Rust ATProto crate

couple readme updates

Orual 91e907ee f499c042

Changed files
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README.md
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Highlights:
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- better value type deserialization helpers
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- service auth implementation
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- XrpcRequest derive Macros
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- more builders in generated api to make constructing things easier (lmk if compile time is awful)
- `AgentSessionExt` trait with a host of convenience methods for working with records and preferences
- Improvements to the `Collection` trait, code generation, and addition of the `VecUpdate` trait to enable that
- A bunch of examples, both in the docs and in the repository