fix: reject same template and output file

[Aias00]

Closed: #1153

Summary

• reject file-based writes where template and output resolve to the same file before opening the output stream
• add regression coverage that original template bytes remain unchanged and distinct files still work

Verification

• ./mvnw -pl fesod-sheet -Dmaven.test.skip=false -DskipTests=false -Dtest=WriteWorkbookHolderOutputStreamTest#writeRejectsSameTemplateAndOutputFileWithoutTruncatingTemplate+writeAllowsDistinctTemplateAndOutputFiles test
• ./mvnw -pl fesod-sheet spotless:check