Fix remaining TODOs regarding work score

[Alex6323]

• SimpleTokenScheme work score (TIP-45: IOTA 2.0 Transaction Payload tips#147 (review))
• CandidacyAnnouncementPayload work score computation (cleared up in discussion, current impl is correct)
• UnlockCondition work score (cleared up in discussion, current impl is correct)
• Actually compute and set the mana in the Block/BasicBlock. Should we pass the RMC to the block builder, determine the block's work score in the finish method? (Calculate and set max_burned_mana field #1610)
• Clarify whether we compute the work score for the Block, but then adapt the max_burned_mana field of its contained BasicBlock? (Calculate and set max_burned_mana field #1610)
• Clarify whether the work score of an output is still offset'ed by the WorkScoreParameters::offset param (TIP-45: IOTA 2.0 Transaction Payload tips#147 (comment))