Remove (frozen) slotsPerArchivedPoint field in favor of config read

[syjn99]

What type of PR is this?

Other

What does this PR do? Why is it needed?

Small refactor. StateManager holds slotsPerArchivedPoint which is fixed in the runtime as params.BeaconConfig().SlotsPerArchivedPoint, and there's no mutation on this field. Rather than holding it and passing it as arguments, just read the global configuration value.

For the testing side, like what we have been doing, mutate the config like:

	slotsPerArchivedPoint := primitives.Slot(128)
	params.SetupTestConfigCleanup(t)
	cfg := params.BeaconConfig().Copy()
	cfg.SlotsPerArchivedPoint = slotsPerArchivedPoint
	params.OverrideBeaconConfig(cfg)

Which issue(s) does this PR fix?

N/A

Other notes for review

No functional behavior changes.

Acknowledgements

• I have read CONTRIBUTING.md.
• I have included a uniquely named changelog fragment file.
• I have added a description with sufficient context for reviewers to understand this PR.
• I have tested that my changes work as expected and I added a testing plan to the PR description (if applicable).