test(bench): remove startup timing assumptions

[drewstone]

Problem

Three release checks used elapsed time as a proxy for an event:

• the proposer test slept 30 ms and assumed both authors had started;
• three real container checks inherited a 5 second test timeout;
• the process cleanup check sent SIGTERM after 60 ms, before Node had reliably installed its handler.

Under parallel CI load, valid behavior could fail solely because startup took longer.

Change

• Both proposer authors now meet at a promise barrier. A serial implementation cannot complete, while a concurrent implementation does not depend on machine speed.
• The three container checks allow 60 seconds for their real process boundary.
• The process cleanup check allows one second for Node startup before sending SIGTERM.

Production code is unchanged.

Proof

On commit 72d5c36:

• build completed;
• the three changed suites passed: 3 of 3 files, 71 of 71 tests;
• the initial command without a build and fixture identity flag failed only during setup, then the normal built test path passed;
• merge-tree against current origin/main produced tree 86dc03504808d085cc37b9c9eb78cf0f976101e6 with no conflict.