Function build_session_term_maps 

pub fn build_session_term_maps(
    session_contents: &[Vec<&str>],
    tokenizer: &Tokenizer,
    prefilter_config: &PrefilterConfig,
) -> Vec<HashMap<String, usize>>

Build per-session term-count maps by pre-filtering, tokenizing, and computing n-gram term counts for each session’s entries.

Each inner Vec<&str> represents the raw content strings for one session. The resulting maps are suitable as input to compute_recurrence.