Add stats collector interface and impl

[pnwpedro]

Description

• Add Stats class that presents an aggregate view of QueryStats
• Add StatsCollector interface
• Add StatsCollectorImpl as a default implementation
• Add TestStatsCollectorImpl

This does NOT wire anything into the client yet.

Motivation and context

BT-4971

We need a class to aggregate query stats that's thread safe and can be instantiated per client. This handles stats tracking for pagination and other use cases where query stats from queries performed at lower levels aren't easily accessible, or where customers which to track stats through a single pane.

How was the change tested?

• Added unit tests

Screenshots (if appropriate):

Change types

• • Bug fix (non-breaking change that fixes an issue)
• • New feature (non-breaking change that adds functionality)
• • Breaking change (backwards-incompatible fix or feature)

Checklist:

• • My code follows the code style of this project.
• • My change requires a change to Fauna documentation.
• • My change requires a change to the README, and I have updated it accordingly.

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