MLv2 metadata calculation validation (#29956)

* Add QP test middleware to validate converted pMBQL queries against MLv2 schema

* Revert 'fix' for #29944

* Fix ups

* Hack

* Fix final test failure

* Remove unused namespace

* MLv2 metadata calculation validation

* Handful of test fixes 

* Fix Kondo warning

* Skip #29958

* Don't barf when metadata is missing

* Skip percentile tests

* Update skip rule for #29910 to skip `:convert-timezone` with string literal date