Poc: expose group hash feedback from GroupValues

[Rachelint]

Which issue does this PR close?

Part of hash aggregate repartition POC.

Rationale for this change

This POC prepares GroupValues for partition-aware partial aggregate output. The partial aggregate output path needs to know which input rows created new groups, and the hash for those rows, so it can later route newly-created group ids to target partitions without relying on a separate repartition + coalesce pipeline.

What changes are included in this PR?

• Extend GroupValues::intern to fill per-row hashes and optionally return the input rows that created new groups.
• Keep hash calculation inside GroupValues implementations.
• Wire reusable hash/new-group-row buffers through aggregate hash table and row-hash paths.
• Update existing call sites and benchmarks to the new intern signature.

Are these changes tested?

Yes:

• cargo fmt --all
• cargo clippy --all-targets --all-features -- -D warnings
• cargo test -p datafusion-physical-plan group_values --lib

[github-actions]

Thank you for opening this pull request!

Reviewer note: cargo-semver-checks reported the current version number is not SemVer-compatible with the changes in this pull request (compared against the base branch).

Details

     Cloning apache/main
    Building datafusion-physical-plan v54.0.0 (current)
       Built [  75.939s] (current)
     Parsing datafusion-physical-plan v54.0.0 (current)
      Parsed [   0.134s] (current)
    Building datafusion-physical-plan v54.0.0 (baseline)
       Built [  39.856s] (baseline)
     Parsing datafusion-physical-plan v54.0.0 (baseline)
      Parsed [   0.137s] (baseline)
    Checking datafusion-physical-plan v54.0.0 -> v54.0.0 (no change; assume patch)
     Checked [   0.587s] 223 checks: 222 pass, 1 fail, 0 warn, 30 skip

--- failure trait_method_parameter_count_changed: pub trait method parameter count changed ---

Description:
A trait method now takes a different number of parameters.
        ref: https://doc.rust-lang.org/cargo/reference/semver.html#trait-item-signature
       impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.48.0/src/lints/trait_method_parameter_count_changed.ron

Failed in:
  GroupValues::intern now takes 4 instead of 2 parameters, in file /home/runner/work/datafusion/datafusion/datafusion/physical-plan/src/aggregates/group_values/mod.rs:102

     Summary semver requires new major version: 1 major and 0 minor checks failed
    Finished [ 118.031s] datafusion-physical-plan