Presentation: Fix flaky full stack test

[grigasp]

Fixes #8751.

Couldn't reproduce locally, but my assumption is that when the first of two tests finishes and "deletes" the test imodel, the second test immediately tries to create a new imodel at the same file path, and FS has that file path locked, causing a hang. The change ensures that we use unique file names for each of the tests.

Update: The above assumption was wrong.

[grigasp]

I was wrong...

  ReadWrite
[2025-11-12T15:38:17.005Z] Tests initialized
    Handling read-write operations
Info | BeSQLite | Opening DgnDb out\8008\readwrite-before-each-hook-for-handles-schema-import-during-nodes-request.bim 
Info | BeSQLite | Created file 'C:\agent\_work\1\s\full-stack-tests\presentation\out\8008\readwrite-before-each-hook-for-handles-schema-import-during-nodes-request.bim-hierarchies' 
Warning | core-backend.IModelDb | there are no unsaved changes 
      √ handles schema import during nodes request (897ms)
Warning | core-backend.IModelDb | there are no unsaved changes 
Info | BeSQLite | Opening DgnDb out\8008\readwrite-before-each-hook-for-handles-schema-import-during-content-request.bim 
##[error]The Operation will be canceled. The next steps may not contain expected logs.

will continue looking into this