Handle newer challenge flows more reliably

[subzeroid]

Summary

Instagram challenge flows keep changing, and newer branches are still a frequent source of login failures.

This issue tracks improving handling for newer challenge flows so the library either resolves them correctly or fails with a clear, actionable error instead of a low-level exception.

Problem areas

Recent user reports repeatedly mention:

• /auth_platform/ challenge flows
• UFAC web bloks flows like ufac_www_bloks
• newer checkpoint variants that do not match older challenge_resolve* assumptions
• hard failures where manual verification is required but the error path is unclear

Proposed scope

• audit current challenge_resolve() and challenge_resolve_simple() branches
• explicitly detect newer unsupported/manual flows
• return clearer exceptions and messages for manual-only paths
• avoid misleading fallback behavior when the challenge cannot be solved automatically
• add regression tests for known challenge payload shapes

Definition of done

• newer challenge payloads are identified more reliably
• unsupported/manual flows fail clearly and predictably
• known recent challenge regressions are covered by tests

[subzeroid]

Progress update on #2420 so far:

Implemented challenge-handling fixes and regression coverage in these commits:

• 543d13e: preserve SMS challenge choice across follow-up steps
• 6460bc5: send numeric contact-form challenge choices
• d9a1ad4: send numeric private challenge choices
• a73449d: harden challenge error handling
• ea327d6: avoid Bandit false positive in challenge flow

Covered so far:

• preserve selected SMS/EMAIL method through follow-up challenge steps
• send correct numeric choice payloads in both contact-form and private challenge flows
• improve handling for malformed nested challenge payloads and unsupported challenge types
• accept VerifySMSCodeFormForSMSCaptcha as a valid follow-up verification step
• replace several raw assert paths with clearer ChallengeError / ChallengeRequired flows
• harden change_password, select_contact_point_recovery, and contact-form finalization paths
• add regression tests for recaptcha/select-contact-point/submit-phone-number/unknown-step/contact-form edge cases

Auto CI is green after these changes.