support instrument attribute macros

[BugenZhao]

Signed-off-by: Bugen Zhao [email protected]

[Copilot]

Pull Request Overview

This PR adds support for attribute macros with the new "attributes" feature. The changes include:

• Exporting the instrument attribute macro in src/lib.rs when the "attributes" feature is enabled.
• Adding an example in examples/instrument.rs demonstrating various usages.
• Including integration and expansion tests as well as updating documentation and Cargo.toml configurations.

Reviewed Changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/lib.rs	Adds conditional export for the instrument macro.
examples/instrument.rs	Provides an example demonstrating instrument usage in async functions.
await-tree-attributes/tests/integration.rs	Verifies basic usage, visibility, and attributes for the macro.
await-tree-attributes/tests/expansion.rs	Ensures the attribute expansion works as expected.
await-tree-attributes/src/lib.rs	Implements the instrument attribute macro and argument parsing.
await-tree-attributes/README.md	Updates documentation to include usage examples for the attributes feature.
await-tree-attributes/Cargo.toml	Configures the crate with necessary dependencies and proc-macro feature.
README.md	Documents the new "attributes" feature and provides usage examples.
Cargo.toml	Updates workspace configuration to include the await-tree-attributes member and examples.