refactor(mobile): immich loading overlay (#5320)

* refactor: dcm fixes

* refactor: ImmichLoadingOverlay to custom hook

* chore: dart fixes

* pr changes

* fix: process overlay add / remove in postframecallback

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Co-authored-by: shalong-tanwen <139912620+shalong-tanwen@users.noreply.github.com>
Co-authored-by: Alex Tran <alex.tran1502@gmail.com>

mobile/analysis_options.yaml

@@ -49,7 +49,6 @@ dart_code_metrics:
     # Common
     - avoid-accessing-collections-by-constant-index
     - avoid-accessing-other-classes-private-members
-    - avoid-async-call-in-sync-function
     - avoid-cascade-after-if-null
     - avoid-collapsible-if
     - avoid-collection-methods-with-unrelated-types