Returns an iterator of clock element affiliated with this headline ```rust use orgize::{Org, ast::Headline}; let org = Org::parse(r#"* TODO foo :LOGBOOK: bar CLOCK: CLOCK: [2024-10-12] baz CLOCK: [2024-10-12] [2024-10-12] :END: foo"#); let hdl = org.first_node:: ().unwrap(); assert_eq!(hdl.clocks().count(), 2); ```
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