[TS] Measure source-replayed branch coverage for unknown-call policies

[CaelmBleidd]

Summary

• Add a coverage search that uses CLOSEST_TO_UNCOVERED_RANDOM without a selected return target.
• Persist generated inputs as soon as a completed symbolic state adds entry-function CFG coverage.
• Replay each input in a fresh Node.js process on the original TypeScript and record source statements and exact if branch arms.
• Replay zero-argument functions through a discarded harness sentinel; 63 of the 264 corpus functions have no inputs.
• Derive nested 30/60/120-second coverage checkpoints from one 120-second search; replay time is separate.
• Pin JacoDB to merged revision 873f8e99faf3f1e4736935be96ce1c319985c574.

Validation

• All three CallsCoverageExperimentTest tests passed with the pinned local JacoDB checkout, including exact replay of a zero-argument function.
• A corpus pilot replayed two inputs and confirmed both source if arms with no replay errors.
• The first campaign stopped at a zero-argument replay failure after 60 completed cells. It is preserved separately. A new full paired campaign is running against the fixed commit; results are not included in this PR.

Review focus

• Candidate selection and coverage checkpoint timing.
• Exact replay transport and source mapping.
• Durability and resume behavior of individual cells.