Add partitions_scanned and partitions_total to Statistics

[BohuTANG]

After #3903 checked in, we should add partitions_scanned and partitions_total to Statistics

databend/common/planners/src/plan_statistics.rs

Line 16 in d8cf752

pub struct Statistics {

and show them in the explain:

databend/common/planners/src/plan_display_indent.rs

Lines 207 to 213 in d8cf752

	write!(
	f,
	"ReadDataSource: scan partitions: [{}], scan schema: {}, statistics: [read_rows: {:?}, read_bytes: {:?}]",
	plan.parts.len(),
	PlanNode::display_scan_fields(&plan.scan_fields()),
	plan.statistics.read_rows,
	plan.statistics.read_bytes,

[BohuTANG]

Let me take