Remove unnecessary traits and wrapper types from the query crate

[evenyag]

What type of enhancement is this?

Refactor

What does the enhancement do?

We defined some wrapper types and traits for the query engine

• Expr refactor: replace Expr with datafusion::Expr #3995
• LogicalPlan
• LogicalOptimizer
• PhysicalOptimizer
• PhysicalPlanner
• PhysicalPlan refactor: Remove PhysicalPlan trait and use ExecutionPlan directly #3894

Most implementations simply forward requests to datafusion. Since we are highly coupled with datafusion and have no plan to support another query engine, we could remove these types.

Implementation challenges

For Expr:

greptimedb/src/common/query/src/logical_plan/expr.rs

Lines 22 to 27 in d997463

	/// Central struct of query API.
	/// Represent logical expressions such as `A + 1`, or `CAST(c1 AS int)`.
	#[derive(Clone, PartialEq, Eq, Hash, Debug)]
	pub struct Expr {
	df_expr: DfExpr,
	}

We could simply remove the Expr and re-export datafusion's Expr

pub use datafusion_expr::expr::Expr;

The LogicalPlan only has one variant so we can replace it with datafusion's LogicalPlan. But we also need to refactor methods of the enum so they can take datafusion's LogicalPlan as input.

greptimedb/src/query/src/plan.rs

Lines 35 to 38 in d997463

	#[derive(Clone, Debug)]
	pub enum LogicalPlan {
	DfPlan(DfLogicalPlan),
	}

We could also remove adapters like the DfPhysicalPlanAdapter if we remove the PhysicalPlan.

Many places use Expr, LogicalPlan, and PhysicalPlan. We might need to refactor them in different PRs.