fix: [L05] Enabling token for Liquidity provisioning should not reset lastLpFeeUpdate

[nicholaspai]

Issue:

• [L05] Liquidity provisioning can skew fee assessments
  • In the HubPool contract the enableL1TokenForLiquidityProvision function allows the contract
    owner to enable an l1token to be added to the protocol for liquidity pooling.
  • This is allowed even if the l1token is already currently enabled.
  • As this function also sets the lastLpFeeUpdate variable to the then-current block.timestamp,
    enabling an already enabled token will skip over the period of time since lastLpFeeUpdate was last
    set. As a result, any LP fees that should have been assessed for that time period would simply never be
    assessed.
  • Consider reverting if this function is called for an l1token that is already enabled.

Solution:

• Only set lastLpFeeUpdate upon first enabling

[mrice32]

LGTM!