feat(router): make atenet timeouts configurable

[Falven (Falven)]

Overview

This PR makes the atenet router timeout budgets configurable while preserving the current defaults.

Motivation

Some actor resume paths can exceed the current hard-coded ext_proc and route budgets. When that happens, Envoy can time out request processing before the router finishes the resume path. Operators should be able to tune these budgets per environment without recompiling the router.

Implementation

• Add --extproc-timeout with the existing 5s default for Envoy ext_proc gRPC and message processing.
• Add --actor-resume-timeout with the existing 15s default for actor resume calls made during request routing.
• Add --route-timeout with the existing 10s default; 0s disables the Envoy route timeout.
• Thread configured durations through router startup, xDS, ext_proc, and ActorResumer.
• Add router tests for defaults, overrides, disabled route timeout, and actor resume deadline propagation.

Related to #166.

Verification

• GOTOOLCHAIN=go1.25.0+auto GOWORK=off go test ./cmd/atenet/internal/app/router
• Appropriate changes to documentation are included in the PR

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