feat!: allow ProjectionExec to take general inputs

[iajoiner]

Please be sure to look over the pull request guidelines here: https://github.com/spaceandtimelabs/sxt-proof-of-sql/blob/main/CONTRIBUTING.md#submit-pr.

Please go through the following checklist

• The PR title and commit messages adhere to guidelines here: https://github.com/spaceandtimelabs/sxt-proof-of-sql/blob/main/CONTRIBUTING.md. In particular ! is used if and only if at least one breaking change has been introduced.
• I have run the ci check script with source scripts/run_ci_checks.sh.

Rationale for this change

We need to make it possible to compose ProjectionExec with ProofPlans.

What changes are included in this PR?

• replace TableExpr in ProjectionExec with Box<DynProofPlan>

Are these changes tested?

Yes.

[iajoiner]

Replacing #377 since GitHub was stuck

[JayWhite2357]

Suggested change

	let mut columns = self.input.get_column_references();
	return self.input.get_column_references();

[iajoiner]

You are right. Projection should result in all output column refs also being input ones.

[JayWhite2357]

Suggested change

	let t = "PLACEHOLDER_SCHEMA.PLACEHOLDER_TABLE".parse().unwrap();
	let mut accessor = OwnedTableTestAccessor::<InnerProductProof>::new_empty_with_setup(());
	accessor.add_table(t, data, 0);
	let ast = projection(cols_expr_plan(t, &["b"], &accessor), tab(t));
	let ast = projection(
	cols_expr_plan(t, &["b"], &accessor),
	table_exec(
	t,
	vec![
	ColumnField::new("a".parse().unwrap(), ColumnType::BigInt),
	ColumnField::new("b".parse().unwrap(), ColumnType::BigInt),
	],
	),
	);
	let t = "sxt.t".parse().unwrap();
	let accessor = OwnedTableTestAccessor::<InnerProductProof>::new_from_table(t, data, 0, ());
	let ast = projection(
	vec![AliasedDynProofExpr {
	expr: DynProofExpr::Column(ColumnExpr::new(ColumnRef::new(
	"PLACEHOLDER_SCHEMA.PLACEHOLDER_TABLE".parse().unwrap(),
	"b".parse().unwrap(),
	ColumnType::BigInt,
	))),
	alias: "b".parse().unwrap(),
	}],
	table_exec(
	t,
	vec![
	ColumnField::new("a".parse().unwrap(), ColumnType::BigInt),
	ColumnField::new("b".parse().unwrap(), ColumnType::BigInt),
	],
	),
	);