chore: release fastrace-opentelemetry v0.18.0

[andylokandy]

Summary

Prepare fastrace-opentelemetry v0.18.0 for release.

This release includes the OpenTelemetry 0.32.0 dependency upgrade and refreshes the README dependency example.

[Copilot]

Pull request overview

Prepares the fastrace-opentelemetry crate for the v0.18.0 release, aligning documentation and metadata with the already-upgraded OpenTelemetry 0.32.0 workspace dependencies.

Changes:

• Bump fastrace-opentelemetry crate version to 0.18.0 (and reflect in Cargo.lock).
• Add a v0.18.0 section to the crate changelog noting the OpenTelemetry 0.32.0 upgrade.
• Update the README dependency snippet to reference fastrace-opentelemetry = "0.18".

Reviewed changes

Copilot reviewed 3 out of 4 changed files in this pull request and generated no comments.

File	Description
fastrace-opentelemetry/README.md	Updates the dependency example to the new crate version.
fastrace-opentelemetry/CHANGELOG.md	Adds the v0.18.0 release entry.
fastrace-opentelemetry/Cargo.toml	Bumps the crate version to 0.18.0.
Cargo.lock	Updates the locked version for fastrace-opentelemetry to 0.18.0.

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