chore(s3vectors): [WRA-10] change custom type embd name to s3vec

[burmecia]

What kind of change does this PR introduce?

This PR is to change custom type embd name to s3vec. We'd prefer to use s3 as a prefix so we can standardise on anything else that the s3 team adds in the future.

What is the current behavior?

N/A

What is the new behavior?

N/A

Additional context

This PR also replaced s3vec::from with s3vec::try_from to guard null pointer.

[Copilot]

Pull Request Overview

This PR renames the custom PostgreSQL type from embd to s3vec to standardize naming with the s3 prefix for future S3 team additions. Additionally, it enhances safety by converting bytea pointer conversions from From to TryFrom with null pointer guards.

• Renamed custom type embd to s3vec throughout the codebase
• Renamed related functions: embd_distance → s3vec_distance, embd_knn → s3vec_knn
• Added null pointer safety by implementing TryFrom for bytea pointer conversions
• Updated version from 0.1.0 to 0.1.1

Reviewed Changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
wrappers/src/fdw/s3vectors_fdw/s3vec.rs	Renamed struct from Embd to S3Vec, converted bytea pointer conversion from From to TryFrom with null check, renamed functions
wrappers/src/fdw/s3vectors_fdw/s3vectors_fdw.rs	Updated import, type references, version number, and refactored query_vectors to use try_from for bytea pointers while keeping from for AWS SDK types
wrappers/src/fdw/s3vectors_fdw/tests.rs	Updated function name in test query from embd_distance to s3vec_distance
wrappers/src/fdw/s3vectors_fdw/mod.rs	Renamed module from embd to s3vec and added new error variant for invalid s3vec values
wrappers/src/fdw/s3vectors_fdw/README.md	Added version 0.1.1 changelog entry documenting the type name change
docs/catalog/s3vectors.md	Comprehensively updated documentation replacing all embd references with s3vec in types, examples, and descriptions

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