feat(tracer): add deterministic preflight checks

[TrevorBasinger]

This PR adds deterministic tracer preflight support to roar and enforces it before workload launch.

Specifically, it:

• adds strict preflight checks for ebpf, preload, and ptrace
• adds native --preflight --json support to the Rust tracer binaries
• updates roar tracer check to use strict preflight, with --json and --command
• makes roar run / roar build fail before launching the workload when the configured tracer cannot work
• preserves auto fallback behavior only among backends that already passed strict preflight

This is intentionally a single-PR implementation focused on deterministic early failure rather than best-effort runtime attach.

Why

We hit a real case where tracer startup looked viable until attach time, then failed late and opaquely:

• roar-tracer-ebpf: failed to attach 'sys_enter_open' ... No such file or directory

That made it too easy for roar to start a workload even when the tracer was known not to be viable on the current
machine/kernel/backend combination.

This PR moves that failure earlier and makes it explicit:

• backend readiness is checked before workload launch
• roar tracer check uses the same strict contract
• native tracers own their own backend-specific validation