Track cpu usage metrics for query execution

[joshua-spacetime]

Description of Changes

Tracks the number of rows scanned and the number of index seeks performed during query execution.

It does not track any byte-level metrics since that depends on #2098.

API and ABI breaking changes

None

Expected complexity level and risk

2

Note, this patch depends on #2130.

Computing and recording the metrics themselves was pretty straightforward, however the previous tuple at a time execution model was not suitable for tracking operator-level metrics, hence it was necessary to employ a new execution model.

Testing

A current test was updated to assert on index seek metrics

[Centril]

How does this affect the subscription benchmarks?

[joshua-spacetime]

@Centril the impact for these is negligible.

full-join        time:   [91.830 µs 92.193 µs 92.510 µs]
                 change: [-1.6552% -1.2958% -0.9618%] (p = 0.00 < 0.05)
                 Change within noise threshold.

However once we introduce "bytes scanned" for example, I fully expect the difference will no longer be negligible.