chore: prepare for releasing 0.30.0

[tisonkun]

No description provided.

[Copilot]

Pull request overview

Prepares the workspace for the 0.30.0 release by bumping crate versions across the workspace and updating release documentation, while also tightening docs/lint configuration for newly externalized crates.

Changes:

• Bump logforth to 0.30.0 and align workspace member crate versions to 0.4.0.
• Add docs.rs configuration and enforce missing_docs for logforth-filter-rustlog and logforth-diagnostic-task-local.
• Add a 0.30.0 entry to CHANGELOG.md.

Reviewed changes

Copilot reviewed 20 out of 20 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
Cargo.toml	Updates workspace dependency versions to match the release (0.30.0 / 0.4.0).
CHANGELOG.md	Adds the 0.30.0 release section/date.
logforth/Cargo.toml	Bumps main crate version to 0.30.0.
core/Cargo.toml	Bumps logforth-core to 0.4.0.
appenders/async/Cargo.toml	Bumps crate version to 0.4.0.
appenders/fastrace/Cargo.toml	Bumps crate version to 0.4.0.
appenders/file/Cargo.toml	Bumps crate version to 0.4.0.
appenders/journald/Cargo.toml	Bumps crate version to 0.4.0.
appenders/opentelemetry/Cargo.toml	Bumps crate version to 0.4.0.
appenders/syslog/Cargo.toml	Bumps crate version to 0.4.0.
bridges/log/Cargo.toml	Bumps crate version to 0.4.0.
diagnostics/fastrace/Cargo.toml	Bumps crate version to 0.4.0.
diagnostics/task-local/Cargo.toml	Bumps crate version to 0.4.0.
diagnostics/task-local/src/lib.rs	Enables docs.rs doc_cfg gating and denies missing docs.
filters/rustlog/Cargo.toml	Bumps crate version to 0.4.0 and adds docs.rs metadata.
filters/rustlog/src/lib.rs	Enables docs.rs doc_cfg gating and denies missing docs.
layouts/text/Cargo.toml	Bumps crate version to 0.4.0.
layouts/logfmt/Cargo.toml	Bumps crate version to 0.4.0.
layouts/json/Cargo.toml	Bumps crate version to 0.4.0.
layouts/google-cloud-logging/Cargo.toml	Bumps crate version to 0.4.0.

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