Fix typo in 3rdparty directory name: possionrecon -> poissonrecon

[add-uos]

Summary

• Rename 3rdparty/possionrecon/ to 3rdparty/poissonrecon/ (correct spelling of Poisson)
• Update the include path in find_dependencies.cmake

Changes

File	Change
3rdparty/possionrecon/	Renamed to 3rdparty/poissonrecon/
3rdparty/possionrecon/possionrecon.cmake	Renamed to 3rdparty/poissonrecon/poissonrecon.cmake
3rdparty/find_dependencies.cmake	Updated include path
CHANGLOGE.md	Updated changelog

Test Plan

• CMake configuration references are unchanged (target names, variables remain ext_poisson / POISSON_INCLUDE_DIRS)
• No logic change, only directory rename

Fixes #7501

[update-docs]

Thanks for submitting this pull request! The maintainers of this repository would appreciate if you could update the CHANGELOG.md based on your changes.