Migration: LegacyPooledStaking changes & asserts in migration.js & scripts

[danoctavian]

Context

Issues:

Pricing assertions + any other assertions for StakingPools: #608
Call pushRewards: #722

Changes proposed in this pull request

This change fixes the assertions around migrated products and their prices in V2 pools.

A read function is added to LegacyStakingPool that serves only 1 purpose: to check the validity of the migrated prices. (it's a view so won't affect anything else).

Test plan

Update and run the fork test.

Checklist

• Rebased the base branch
• Attached corresponding Github issue
• Prefixed the name with the type of change (i.e. feat, chore, test)
• Performed a self-review of my own code
• Followed the style guidelines of this project
• Made corresponding changes to the documentation
• Didn't generate new warnings
• Didn't generate failures on existing tests
• Added tests that prove my fix is effective or that my feature works

Review

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