[avalanche] Add transaction management to the processor core

Summary:
This puts the transactions in parity with the blocks and proofs. Note the the sorting and filtering is dumb for now and needs to be expanded, which is not a problem since we don't add any transaction to reconcile yet.

Depends on D13066 and D13067.

Test Plan:

ninja all check-all

Reviewers: #bitcoin_abc, sdulfari

Reviewed By: #bitcoin_abc, sdulfari

Subscribers: sdulfari

Differential Revision: https://reviews.bitcoinabc.org/D13068