Function draw_statuscolumn 

fn draw_statuscolumn(
    current_buffer_type: &str,
    cur_lnum: &str,
    metas: impl Iterator<Item = ExtmarkMeta>,
    opts: Option<Opts>,
) -> String

Constructs the status column string for the current line.

Assumptions

• metas yields at most a small number of items (typical per-line sign density is low).
• Caller has already restricted extmarks to those relevant for the line being drawn.

Rationale

• Single pass selects highest severity and first git sign to avoid repeated scans.
• Early break once an Error (rank 5) and a Git sign are both determined prevents unnecessary iteration.
• Manual string building reduces intermediate allocation versus collecting sign fragments.

Performance

• Allocates once with a conservative capacity heuristic (lnum.len() + 64).
• O(n) over metas, short-circuiting when optimal state reached.
• Rank computation is a simple match with small constant cost.