ConstB2 native listing has no server-side cap, so these scans stop after this
budget and return truncated / lower-bound results rather than running for
minutes. Exported as the single source of truth so both scan paths — and the
deadline coverage tests — share one value instead of hand-copying the
literal. (The report-CSV scan tracks its own REPORT_SCAN_LIMITS.maxElapsedMs
budget, which is a separate subsystem that merely happens to share this
value.)
Wall-clock budget for the bounded native LIST scans behind
b2_list_largest_filesandb2_unfinished_uploads.