Update README to include buffer and prepared geometry features

[peterstace]

Description

Update the README to document two recently added features:

• Buffer: buffer with configurable end cap styles, join styles, and single-sided mode.
• Prepared geometries: preprocess a geometry for efficient repeated spatial predicate evaluation.

Also updated the JTS attribution paragraph to mention that buffer and prepared geometry operations are powered by the JTS port.

Check List

Have you:

• Added unit tests? N/A (documentation only change)

• Add cmprefimpl tests? (if appropriate?) N/A

• Updated release notes? (if appropriate?) N/A

• Updated the README.md (if new functionality is added?) Yes, this is the README update.

Related Issue

• N/A

Benchmark Results

• N/A (documentation only change)

[Copilot]

Pull request overview

Updates the project README to document recently added geometry capabilities (buffering and prepared geometries) and clarifies that these operations are powered by the JTS port.

Changes:

• Document buffer support (cap/join styles and single-sided mode).
• Document prepared geometries for efficient repeated predicate evaluation.
• Update the JTS attribution paragraph to include buffer and prepared geometry operations.

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