* refactor: move inner classes to top level

Move the gRPC-related inner classes from AbstractResultSet to
top-level classes, so they are easier to modify and maintain.

This change only contains modifications that are needed to move
these inner classes. There are no functional changes.

* feat: support lazy decoding of query results (#2847)

* feat: support lazy decoding of query results

Adds an option for lazy decoding of query results. Currently, all values
in a query result row are decoded from protobuf values to plain Java
objects at the moment that the result set is advanced to the next row.
This means that all values are decoded, regardless whether the
application actually fetches these or not.

Lazy decoding also enables the possibility for (internal) consumers
of a result set to access the protobuf value before it is converted
to a plain Java object. This for example allows ChecksumResultSet to
calculate the checksum based on the protobuf value, instead of a
Java object, which can be more efficient.

* fix: add null check

* perf: calculate checksum using protobuf values (#2848)

* perf: calculate checksum using protobuf values

* chore: cleanup

* test: remove unrelated test

* fix: undo change to public API

* chore: cleanup|

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