SYSTEM transactions in the HUB

[OlivierBBB]

This PR contains a major overhaul of the HUB module's low level constraints. This is required in order to properly deal with system transactions along side user transactions.

TODOs:

• replace ABS_TX_NUM by the appropriate transaction number, likely a mixture of
  • TOTL_TRANSACTION_NUMBER
  • USER_TRANSACTION_NUMBER
• in particular update lookups
  • the columns may have changed
  • the selectors are different now e.g. for HUB -> TXN_DATA we should now use USER ∙ TXN
• rename TXN_DATA to USER_TXN_DATA
• re-insert and update spec of SYST_TXN_DATA
• add the spec for
  • TX_SKIP ∧ SYSI
    • bla ∧ TXN ∧ EIP_4788_⚜️
    • bla ∧ TXN ∧ EIP_2935_⚜️
  • TX_SKIP ∧ USER
  • TX_SKIP ∧ SYSF
  • TX_FINL (we need to finish on a CON row)

Both EIP_4788 and EIP_2935 will be of the form

TXN
ACC
STO
CON

The TX_SKIP ∧ USER case will be

TXN
ACC
ACC
ACC
CON

The TX_SKIP ∧ SYSF case will be

TXN
CON

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[cla-assistant]

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_{You have signed the CLA already but the status is still pending? Let us recheck it.}