MSVC fix for hostile fixed-base lifecycle test on main

[shrec]

What

• Fixed the remaining windows (Release) blocker on main: exploit_ctx_lifecycle_hostile had several fast::FixedBaseConfig locals that were left uninitialized.
• GCC/Clang happened to pass, but MSVC picked up garbage flags and made [8] Sign-verify roundtrip after precompute init fail intermittently.
• All hostile fixed-base test configs are now value-initialized, so the audit uses deterministic runtime settings on every platform.

Numbers

• Local hostile regression: 58 passed, 0 failed
• Commit: fcaa8327

How to get it

• Branch: main
• Commit: fcaa8327
• A fresh CI run was triggered automatically on push.