feat: remove UDS auth

[NathanFlurry]

Summary

• Remove UDS auth flow: Token-based authentication over Unix domain socket is unnecessary — the socket dir has 0700 permissions + 128-bit random suffix. Removes SECURE_EXEC_V8_TOKEN, authenticate_connection, constant_time_eq, and related tests from both Rust and TS.
• Burst + staggered benchmarks: New bench modes matching the computesdk pattern — burst fires N runtimes simultaneously, staggered launches with configurable delay + ramp profile.
• Fix 15ms createNodeDriver() overhead: collectOverlayAllowedRoots does synchronous readdirSync + realpathSync on every symlink in node_modules (~20ms in large monorepos). Benchmarks and docs now reuse the driver instance.
• Warm pool default increased to 5 for better p95 under staggered load.
• IPC trace instrumentation: SECURE_EXEC_TRACE_IPC=1 env var enables per-execution phase timing on both TS and Rust sides.

Benchmark results (sequential cold start, 100 iterations)

	p50	p95	p99
No pool	6.17ms	8.82ms	14.12ms
Pool of 5	4.02ms	5.55ms	6.23ms

Test plan

• 128 TS tests pass (2 auth tests removed)
• 82 Rust tests pass (7 auth/constant_time tests removed)
• All three benchmarks run successfully (coldstart, burst, staggered)

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