[identity] Support tuples in device list verification

Summary:
Addresses ENG-10232 and verification part of ENG-10239.
Updated verification function to allow tuples if keyserver device ID is some.

Original "strict form" breaks existing clients if they're keyserver owners (so breaks dev experience) so implemented an opt-in flag, of which removal is tracked in ENG-10414.

Test Plan:
Both strict/non-strict tested on staging:

• No behavior change when no keyserver present
• When keyserver is present, devce lists of length 2 are allowed
  • Additionally in strict form, keyserver device ID must match and singletons are no longer allowed

Reviewers: kamil

Reviewed By: kamil

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D14490