`provekit/common/src/sparse_matrix`: Make it default infinite size instead.

[recmo]

On 2025-08-29 in 2a57572 “Merge pull request #153 from worldfnd/px/refactor”:

Make it default infinite size instead.

    pub const fn num_entries(&self) -> usize {
        self.values.len()
    }

    pub fn grow(&mut self, rows: usize, cols: usize) {
        // TODO: Make it default infinite size instead.
        assert!(rows >= self.num_rows);
        assert!(cols >= self.num_cols);
        self.num_rows = rows;
        self.num_cols = cols;
        self.new_row_indices.resize(rows, self.values.len() as u32);

From provekit/common/src/sparse_matrix.rs:59