Fix: implement special treatment in abacuslite I/O on the SCF unconverged case

[kirk0830]

Reminder

• Have you linked an issue with this pull request?
• Have you added adequate unit tests and/or case tests for your pull request?
• Have you noticed possible changes of behavior below or in the linked issue?
• Have you explained the changes of codes in core modules of ESolver, HSolver, ElecState, Hamilt, Operator or Psi? (ignore if not applicable)

Linked Issue

Fix #7194

Unit Tests and/or Case Tests for my changes

• two unit test cases are added in legacyio.py and latestio.py, respectively

What's changed?

• add two functions, one for searching the information how the iteration proceeds, one for filtering out the final information

Any changes of core modules? (ignore if not applicable)

• No.