Function validate_span 

pub fn validate_span(
    span: &Span,
    timestamp_range: Option<&Range<UnixTimestamp>>,
) -> ProcessingResult

Validates a span.

A ProcessingResult error is returned when the span is invalid. A span is valid if all the following conditions are met:

• A start timestamp exists.
• An end timestamp exists.
• Start timestamp must be no later than end timestamp.
• A trace id exists.
• A span id exists.