perf: fixed graph update once

[fodzal]

Issue.
In a fixed variable reference graph, when two shadow variables share a source and one
also depends on the other, the shared source enqueues both directly, and updating the first
re-enqueues the second through their edge before dedup catches it. Its supplier then runs twice for
nothing:

@ShadowVariable(supplierName = "durationSupplier") // @ShadowSources("value")
Integer duration;

@ShadowVariable(supplierName = "endTimeSupplier")  // @ShadowSources({ "value", "duration" })
Integer endTime;

value marks duration and endTime directly; duration also marks endTime via the
duration → endTime edge. endTimeSupplier runs twice for the same pass.

Fix. The dedup check happened at enqueue time (visited, seeded from only the first queued
node) instead of at dequeue time. Track updated nodes and check when a node comes out of the
queue instead of when it goes in:

if (updated.get(changedNodeId)) {
    continue;
}

Benchmark. 200 entities, each a chain of 20 shadow ints all sourced from the same genuine
variable and each also depending on the previous link; every move marks all 20 directly and
re-marks 19 of them through the chain:

	before	after
supplier calls / move	~35	20 (exact)
move time, trivial supplier	~3.4 µs	~3.5 µs (noise; overhead dominates)
move time, realistic supplier	~28.3 µs	~18.6 µs (-34%)