fix: support Unity 6000 TreeView and guard async progress reentrancy

[SUWAROW]

No description provided.

[nolimet]

I'm looking at this as a thirdparty and just questioning why other than the affected class are being altered. The lack of a description is worry som

[SUWAROW]

I'm looking at this as a thirdparty and just questioning why other than the affected class are being altered. The lack of a description is worry som

The PR includes two separate changes for practical reasons.
The async fix is applied across multiple runtime and generated files to keep behavior consistent and avoid partial fixes.
The editor change is a small, unrelated import required for compilation with newer Unity versions.

In any case, if the earlier PR that addresses support for newer Unity versions gets merged into main first, I will adjust my changes accordingly. For now, I’m working on the newer unstable Unity versions using a fork build from this commit.