Latency reported when using linked SharedState

[masenf]

Describe the bug
Bert on discord notes that when a state is linked, per-message websocket latency is significantly higher (~5x)

[linear-code]

ENG-10127

[harsh21234i]

hey @masenf
I went through the linked state event path. This looks like a backend latency issue rather than a frontend/websocket
transport issue.

Once _reflex_internal_links is set, each event goes through modify_state_with_links, which can patch linked shared
states and also forces shared-state delta traversal through _always_dirty_substates. That means even events
unrelated to the linked state may pay linked-state overhead per websocket message.

I think the safest next step is to add a focused benchmark comparing the same event before and after linking a
SharedState, then optimize the measured hot path. My initial suspicion is that linked-state patching should become
lazier, or be skipped for handlers that do not access linked state, while preserving fan-out behavior for actual
shared-state mutations.