fix(verilator): select RushB RTL through bbdev

[daiyongyuan]

Summary

• propagate the rushB option through Verilator clean, generation, build, simulation, and batch steps
• select a separate *RushBVerilatorConfig output directory only when RushB is requested
• prefer the project Python environment when building the compiler

Validation

• python3 -m compileall -q api
• exercised by the Buckyball LeNet RushB Verilator end-to-end run