Port `DynamicFilterPhysicalExpr` to use `try_to_proto` / `try_from_proto`

[adriangb]

Sub-issue of #22418. Port DynamicFilterPhysicalExpr to own its protobuf (de)serialization via the try_to_proto / try_from_proto hooks added in #21929. This is the original motivator (#21807) — the goal is not just the hooks but deleting the pub-for-proto scaffolding they were added to support.

Reference: copy the Column migration in #21929. Mind the asymmetry — try_to_proto is a trait override, try_from_proto is an inherent fn.

Where it lives

datafusion/physical-expr/src/expressions/dynamic_filters.rs (crate datafusion-physical-expr).

Steps

1. Add try_to_proto inside the impl PhysicalExpr for DynamicFilterPhysicalExpr block (trait override), feature-gated #[cfg(feature = "proto")].
   ⚠️ Not an inherent impl method — the serializer dispatches through &dyn PhysicalExpr, so an inherent method is silently never called.
2. Add DynamicFilterPhysicalExpr::try_from_proto(node, ctx) and wire it into the matching ExprType::… arm in from_proto.rs.
3. In this same PR, delete the DynamicFilterPhysicalExpr arms from both to_proto.rs and from_proto.rs. Deleting the arm is the only proof the hook is reached.
4. Revert the pub-for-proto scaffolding from proto: serialize and dedupe dynamic filters v2 #21807 in this same PR — Inner, from_parts, inner(), original_children, remapped_children. Now that decode reads the state directly, these should disappear. Deferring this defeats the purpose of the issue. (A ready-to-cherry-pick commit was posted on PR refactor: add try_to_proto / try_from_proto to DynamicFilterPhysicalExpr #22452.)
5. expr_id matters here — this is the one expression that sets it. Make sure try_to_proto preserves it via the encode ctx and that expression IDs stay stable across a roundtrip.

Tests

• The three existing dynamic-filter roundtrip tests must still pass, especially test_dynamic_filter_expression_id_is_stable_between_serializations.
• Add a direct hook test covering both directions and a bad-input case (wrong expr_type / missing child → clean error).
• #[cfg(test)] mod tests at the end of the file (clippy items-after-test-module).

Before you push

• Fill in every section of the PR template.
• cargo fmt --all and cargo clippy --all-targets --all-features -- -D warnings must pass.

Checklist

• try_to_proto in the impl PhysicalExpr block (not inherent), #[cfg(feature="proto")]
• try_from_proto wired into from_proto.rs
• central to_proto.rs + from_proto.rs arms deleted in this PR
• Inner / from_parts / inner() / original_children / remapped_children reverted in this PR
• expr_id preserved; expression-id-stability test passes
• direct hook test incl. bad-input case; test module at end of file
• fmt + clippy -D warnings clean; PR template filled in

[AnuragRaut08]

Hi @adriangb, I'd like to work on this.

I'll wait for #21929 to land and then port DynamicFilterPhysicalExpr following the same Column / BinaryExpr migration pattern.

I’ll also handle reverting the pub-for-proto scaffolding mentioned in the issue once decode reads the state directly.

[adriangb]

Great, I've assigned this to you!