v2.0.0

Other

• use README as crate doc to also test README snippets
• use cargo nextest instead of cargo test
• move option unwrap into datadog_ids
• add missing unit-tests for layer
• increase readability of layer and field logic
• [breaking] introduce custom event sinks to enable testing
• disable certain lints in tests
• introduce nightly formatting options and apply to code
• (deps) only specify minor or patch versions of dependencies when needed
• update and split workflows into multiple files
• add important badges