[SPARK-50655][SS] Move virt col family related mapping into db layer instead of encoder

[anishshri-db]

What changes were proposed in this pull request?

Move virt col family related mapping into db layer instead of encoder

Why are the changes needed?

Keep abstraction clear around ownership and also expose internal/non-internal key metrics correctly.
With this change, we have the following:

• encoder is only responsible for managing encoding based on type such as noPrefix, prefix, range etc
• the onus of maintaining virtual col families is now with the underlying DB layer
• this layer can now also expose metrics for internal as well as non-internal column families

Does this PR introduce any user-facing change?

No

How was this patch tested?

Existing Unit tests

[info] Run completed in 8 minutes, 48 seconds.
[info] Total number of tests run: 305
[info] Suites: completed 1, aborted 0
[info] Tests: succeeded 305, failed 0, canceled 0, ignored 0, pending 0
[info] All tests passed.

Was this patch authored or co-authored using generative AI tooling?

No

[anishshri-db]

cc - @ericm-db @jingz-db - PTAL, thx !