Fix unreachable RT feature submodule revisions

[liuqliang]

Summary

• replace the unreachable driver gitlink with the latest public develop head (a39344e)
• replace the unreachable LLVM gitlink with the latest public feature/ray-tracing head (af17c8b)
• replace the unreachable Spike gitlink with the latest public feature/ray-tracing head (ea005ca)
• leave all .gitmodules URLs unchanged

Root cause

ventus-env@a698c63 references three commits that the repositories named by .gitmodules cannot serve:

• driver c5ce8a7d7c82913b70749b08760405fd9d9381f5
• LLVM 29da3a118b91c50a7e8477193e571b97503d781d
• Spike b1ef3ef36583ffc9a1a420fad16cd6804fe7e050

Fetching each SHA directly returns upload-pack: not our ref, so a fresh recursive checkout cannot reconstruct the feature branch.

This repair intentionally follows the current public upstream heads instead of preserving local-only revisions.

Validation

• confirmed that a698c63 is still the latest upstream feature/ray-tracing head before preparing the change
• confirmed the three old SHAs fail direct fetch from their declared upstream URLs
• confirmed all 13 resulting submodule commits resolve in their declared GitHub repositories
• completed real shallow submodule checkouts for driver and Spike from a fresh clone of the pushed fork branch
• completed a filtered single-branch LLVM clone from the upstream feature/ray-tracing ref and verified HEAD == af17c8b
• ran git diff --check

The unavailable revisions cannot be compared with their replacements because their objects are no longer published. A full recursive checkout/build remains the integration gate before merge; in particular, the large LLVM checkout should run in the normal cached CI/build environment.