Fix tensorboardyt v2 transforms API

[saurabhkthakur]

Fixes #3857

Description

Updated

1. v2 transforms migration
2. net.eval() / net.train()
3. f-string updates
4. stale comment removal

Checklist

• The issue that is being fixed is referred in the description (see above "Fixes #ISSUE_NUMBER")
• Only one issue is addressed in this pull request
• Labels from the issue that this PR is fixing are added to this pull request
• No unnecessary issues are included into this pull request.

[pytorch-bot]

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