Implement tree explain for DataSourceExec

[alamb]

Which issue does this PR close?

• part of [EPIC] Complete SQL EXPLAIN Tree Rendering #14914

Rationale for this change

• See [EPIC] Complete SQL EXPLAIN Tree Rendering #14914

We want to have nice explain plans for users. Let's add some detail to the DataSourceExec

What changes are included in this PR?

• Implement tree explain for DataSourceExec
• Implement for DataSource and FileSource
• Tests

Are these changes tested?

yes

Are there any user-facing changes?

[alamb]

Per the description of TreeRender:

datafusion/datafusion/physical-plan/src/display.rs

Lines 48 to 74 in 3dc212c

	/// TreeRender, displayed in the `tree` explain type.
	///
	/// This format is inspired by DuckDB's explain plans. The information
	/// presented should be "user friendly", and contain only the most relevant
	/// information for understanding a plan. It should NOT contain the same level
	/// of detail information as the [`Self::Default`] format.
	///
	/// In this mode, each line contains a key=value pair.
	/// Everything before the first `=` is treated as the key, and everything after the
	/// first `=` is treated as the value.
	///
	/// For example, if the output of `TreeRender` is this:
	/// ```text
	/// partition_sizes=[1]
	/// partitions=1
	/// ```
	///
	/// It is rendered in the center of a box in the following way:
	///
	/// ```text
	/// ┌───────────────────────────┐
	/// │ DataSourceExec │
	/// │ -------------------- │
	/// │ partition_sizes: [1] │
	/// │ partitions: 1 │
	/// └───────────────────────────┘
	/// ```

TreeRender mode should have only the most relevant details for understanding the high level plan

[alamb]

Likewise, the previous version is too verbose I think

[alamb]

I don't know why there is an extra newline here 🤔

[comphead]

lgtm thanks @alamb

[alamb]

Thanks @comphead

[comphead]

Btw I like this simple approach to calc batch sizes, we can also reuse it in #14510 perhaps to sum up all incoming or outcoming batches.

[comphead]

Thanks again @alamb