refactor(zkvm,gkr): simplify chip finalize flow

[dreamATD]

Summary

This PR simplifies the chip finalize flow by moving layer construction into each chip/layout's finalize implementation, so callers no longer need to manually compute out_evals, build a Layer, and call chip.add_layer(...).

What changed

• Added a shared default_out_eval_groups(...) helper in gkr_iop.
• Updated finalize(...) implementations to directly assemble and return a fully built Chip.
• Removed duplicated caller-side boilerplate in precompile, instruction, and table builders.

Why

This makes the finalize contract simpler and more consistent: callers ask for a finalized chip and receive a ready-to-use one, instead of partially constructing it in multiple places.

Validation

• cargo check
• cargo check --all-targets

[hero78119]

👍 apart from one comment, other LGTM!

[hero78119]

LGTM!