feat(services/core): Implement stat_has_* and list_has_* correctly for services

[geetanshjuneja]

Which issue does this PR close?

Closes #5314.

Rationale for this change

What changes are included in this PR?

Implemented stat_has_* and list_has_* correctly for services
I have removed some redundant code mentioned below

opendal/core/src/services/pcloud/core.rs

Lines 368 to 370 in 86d6c42

	if let Some(size) = content.size {
	md.set_content_length(size);
	}

opendal/core/src/services/pcloud/core.rs

Lines 388 to 390 in 86d6c42

	if let Some(size) = content.size {
	md.set_content_length(size);
	}

Are there any user-facing changes?