fix: more cluster resiliency improvements

[mattjohnsonpint]

Working on cluster resilience. Likely this won't be the last one in this area.

[Copilot]

Pull Request Overview

This PR enhances cluster resilience by adding structured tracing, refactoring discovery, and unifying duration handling.

• Inject Sentry spans across actor lifecycle methods and key helpers
• Refactor cluster discovery into newDiscoveryProvider with a wrapper for tracing
• Introduce getDurationFromEnv and update environment-based timing configuration

Reviewed Changes

Copilot reviewed 10 out of 11 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
runtime/httpserver/health.go	Pass r.Context() into ListLocalAgents
runtime/go.mod	Bump github.com/tochemey/goakt/v3 to v3.6.5
runtime/actors/wasmagent.go	Add spans in PreStart/Receive/PostStop/etc. and reorder buffers init
runtime/actors/subscriber.go	Instrument subscription functions with spans
runtime/actors/misc.go	Add getDurationFromEnv and instrument tell/ask with spans
runtime/actors/cluster.go	Extract discovery logic into newDiscoveryProvider, add duration helpers, and spans
runtime/actors/agents.go	Instrument agent lifecycle APIs with spans; update ListLocalAgents signature
runtime/actors/actorsystem.go	Refactor startup into startActorSystem with retry/backoff and add spans
runtime/actors/actorlogger.go	Remove paused/shutdown filters and simplify logging
CHANGELOG.md	Add entry for v0.18.0-alpha.10

Comments suppressed due to low confidence (2)

runtime/actors/misc.go:81

• Add unit tests for getDurationFromEnv to verify correct behavior when the environment variable is missing, invalid, or zero to prevent regressions.

func getDurationFromEnv(envVar string, defaultValue int, unit time.Duration) time.Duration {

runtime/actors/cluster.go:178

• The new environment variables (e.g. MODUS_CLUSTER_PEER_SYNC_SECONDS, MODUS_CLUSTER_NODES_SYNC_SECONDS) should be documented in the project README or an environment reference to guide operators.

func peerSyncInterval() time.Duration {