KeyLock: add per-job configurable heartbeat timeout in RunOpts

[sotashimozono]

Problem

src/KeyLock.jl has a heartbeat stale threshold, but it is a global constant. For HPC workflows:

• Fast jobs (N=20 DMRG): 60s stale threshold is fine
• Slow jobs (N=100 TPQMPS, chi=128, beta=10): runs 30–90 minutes; a 5-minute stale threshold causes incorrect lock reclamation by other workers

Proposed fix

Add configurable timeouts to RunOpts:

@kwdef struct RunOpts
    heartbeat_interval::Float64 = 30.0   # seconds between heartbeat touches
    stale_threshold::Float64 = 300.0     # seconds before lock is considered stale
    max_retries::Int = 3
    # ... existing fields
end

Pass opts.stale_threshold to KeyLock.is_stale(lock; threshold=...).

Use case

FiniteTemperature.jl Phase 1 TPQ runs at chi=128, N=100, beta=10 can take 30–90 minutes per sample. The current default 5-minute stale threshold causes premature lock reclamation on multi-node HPC runs.