Fix PortAnaRecord crash on duplicate "datetime" level (#1909)

[genisis0x]

Summary

• PortAnaRecord._generate and MultiPassPortAnaRecord.random_init resolved the prediction DataFrame's datetime level by name via index.get_level_values(\"datetime\").
• Some handler/processor chains produce a MultiIndex that carries two levels both named datetime. In that case pandas raises ValueError: 'datetime' occurs multiple times, which is the crash in datetime occurs multiple times #1909.
• Switch both call sites to positional lookup: dt_level = index.names.index(\"datetime\") then index.get_level_values(dt_level). That returns the first datetime level deterministically and survives duplicate names.

Test plan

• New tests/misc/test_record_temp_duplicate_datetime.py builds a MultiIndex with duplicate datetime names and asserts:
  • name-based lookup raises ValueError (precondition)
  • positional lookup returns the expected values
• Existing record-temp unit tests still pass (no behavior change on single-datetime indexes)

Fixes #1909

[genisis0x]

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