feat(cadence-matching): simplify the load calculation for shards

[eleonoradgr]

What changed?
Instead of relying on LoadBalancerHints for load calculation, we rely on a new method QueriesPerSecond, which is only providing the value we are interested in

Why?
This is a more efficient way to get the load, since startWG.Wait() which is invoked in the LoadBalancerHints is stopping until the tasklist is started, but we don't really need to wait at startup, since the load will be 0.

How did you test it?
unit tests

Potential risks
no risk, we are using the same value right now

Release notes

Documentation Changes

[gitar-bot]

Running post-merge workflows

Code Review ✅ Approved

Clean refactoring that simplifies load calculation by adding a direct QPS accessor method, eliminating unnecessary blocking during startup. The change is well-tested and maintains functional equivalence.

Rules ❌ No requirements met

Repository Rules

❌ PR Description Quality Standards: Improve [How did you test it?] with exact test commands (e.g., `go test -v ./service/matching -run TestQueriesPerSecond`). Enhance [Why?] to explain why QueriesPerSecond method was chosen over alternatives. Strengthen [Potential risks] with specific backward compatibility and rollback analysis.

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[gitar-bot]

Updated the PR title to follow conventional commit format: changed from feat [cadence-matching]: to feat(cadence-matching):. The validation check should pass on the next run.

[arzonus]

lgtm 🚀