fix: provide vcd2fst during P2E workload runs

[daiyongyuan]

Summary

• Launch the P2E runtime through bebop's Nix shell so vcd2fst is available when waveform capture is enabled.
• Keep the existing runtime executable and P2E arguments.

Validation

• nix develop -c resolves both vcd2fst and vdbg after sourcing the P2E environment.
• The existing bebop-p2e run p2e --help starts in that shell.
• Python compilation and git diff --check passed.

The failed run produced waveform50951.vcd; it was converted to FST manually. A full FPGA workload has not been rerun with this change.