Function validate_optional_max_count 

pub fn validate_optional_max_count(
    max_count: Option<i32>,
    max_allowed: i32,
    endpoint: &str,
) -> Result<Option<i32>, PageBoundsError>

Validate optional max_count parameters used by history-kline-style calls.

Semantics:

• None and Some(0) mean unbounded/default and normalize to None;
• positive values must be within max_allowed;
• negative values are rejected loudly.