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]

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.

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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.