Caching membership witnesses of contracts breaks interaction after deployment

[sirasistant]

The following sequence fails:

sirasistant@MacBook-Pro-de-Alvaro card_game % aztec-cli deploy \       
 PrivateTokenContractAbi \
  --args 1000000 $ALICE \                 
  --salt 27                                                                              

Contract deployed at 0x266ddc72093a1ca6d32877c37ab92bcffe3c4d14c27c4832352be992e297a29c

sirasistant@MacBook-Pro-de-Alvaro card_game % aztec-cli send transfer \
  --args 500 $BOB \
  --contract-abi PrivateTokenContractAbi \
  --contract-address 0x266ddc72093a1ca6d32877c37ab92bcffe3c4d14c27c4832352be992e297a29c \
  --private-key 0x2153536ff6628eee01cf4024889ff977a18d9fa61d0e414422f7681cf085c281

Transaction has been mined
Transaction hash: 23b37f59fb14f4c1f504ef6266059deafbe1a81292cd7522ab2930422619dc0b
Status: mined

Block number: 3
Block hash: f0477801ee3a1397fc3d258fb8b5c8302e3c27e38cb3e615b04553d09a6cd0f4
sirasistant@MacBook-Pro-de-Alvaro card_game % aztec-cli deploy \       
 PrivateTokenContractAbi \
  --args 1000000 $ALICE \                 
  --salt 28                                                                              

Contract deployed at 0x1e2af112bb60040672cfef526dfaacd03857fe1fccf78b0a81717dbf0f0fcbaa

sirasistant@MacBook-Pro-de-Alvaro card_game % aztec-cli send transfer \
  --args 500 $BOB \       
  --contract-abi PrivateTokenContractAbi \
  --contract-address 0x1e2af112bb60040672cfef526dfaacd03857fe1fccf78b0a81717dbf0f0fcbaa \
  --private-key 0x2153536ff6628eee01cf4024889ff977a18d9fa61d0e414422f7681cf085c281
Error in command execution
NoRetryError: computed_contract_tree_root doesn't match purported_contract_tree_root

On a fresh sandbox, deploy one contract with a specific salt, send a transaction to it, deploy the same ABI with a different salt, try to send a transaction to it, it doesn't compute correctly the contract tree root

The cause is that we are caching membership witnesses, so after the first transfer the witness for the account contract and the token contract is cached. Then we deploy another contract and the witnesses are invalid. We should switch to only cache contract indexes, that is the only data that is both expensive to calculate and shouldn't change.