Function check_yaml_budget 

pub fn check_yaml_budget(
    input: &str,
    budget: Budget,
    scope: EnforcingPolicy,
) -> Result<BudgetReport, ScanError>

Check an input &str against the given Budget.

Parameters:

• input: YAML text (UTF-8). If you accept non-UTF-8, transcode before calling.
• budget: limits to enforce (see Budget).

Returns:

• Ok(report) — report.breached.is_none() means within budget. If report.breached.is_some(), you should reject the input.
• Err(ScanError) — scanning (lexing/parsing) failed.

Note:

• This is streaming and does not allocate a DOM.
• Depth counts nested SequenceStart and MappingStart.
• Standalone budget checks do not receive Options; merge keys are counted as if merge expansion is enabled, preserving historical behavior.