feat(erpc:PLA-695): pluggable routing strategies and capability-aware filtering

[0x666c6f]

Summary

• add capability tags to upstream config (upstreams[].capabilities) and method requirements (methods.definitions.<method>.requires)
• enforce capability matching in network upstream selection to prevent routing a method to incompatible upstreams
• add routing strategy registry and new strategies: latency-aware, cost-aware, rendezvous
• keep default behavior unchanged (score-based)
• add focused tests for capability normalization/filtering and strategy behavior/distribution

Validation

• go test ./common -run 'Test(NormalizeCapabilityTags|HasAllCapabilities|IsValidCapabilityTag)$' -count=1
• go test ./upstream -run 'TestUpstreamsRegistry_(RoundRobinStrategy|LatencyAwareStrategy|CostAwareStrategy|RendezvousStrategyDeterministicDistribution)$' -count=1
• go test ./erpc -run 'Test(FilterUpstreamsByRequiredCapabilities|NetworkForward_MethodCapabilitiesMismatchPrevented)$' -count=1
• go test ./erpc -run '^$' -count=1
• go test ./erpc -run 'TestNetwork_Forward_InfiniteLoopWithAllUpstreamsSkipping|TestNetwork_Forward_BatchSelectionCacheReuse' -count=1
• make agent-check
• make agent-review-load