Failure of sublayout verification leads to failure of entire verification routine

[adityasaky]

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Description of issue or feature request:

#19 introduced sublayout verification capabilities, which closely resemble the reference implementation. Currently, the overall verification process fails as soon as sublayout verification fails at some stage, instead of proceeding with other steps and checking for threshold value later.

Expected behavior:

The implementation must continue the verification routine and consider summary links only from successfully verified sublayouts. The verification routine can then check if threshold value is met further down the line.

For more details: #19 (comment)