Enhance security of "ProxyTargetApprove" by using a push model

[PaulRBerg]

Copy-pasting Dirk's feedback in https://github.com/cantinasec/review-pr-sablier/issues/1#issuecomment-1691498820:

Description: PR 161 introduces the use of token approval/allowances for the proxy contract to create streams rather than use explicit Permit2 signatures.The intended use case is for Safe users to avoid having to let every cosigner need to sign the permit2 offline sig and use a Safe multi-send to batch an approve on the ERC20 token and create the stream in the same transaction.

However some non Safe users may be inclined to use approvals over the permit2 use case going even so far as to use infinite approvals to save gas and to ease the Ux.
The risk is that remaining balances on token approvals (or max approvals) can get abused by rogue envoys (or compromised contracts of those are set as envoys) to create streams to arbitrary receivers.

This wasn't the case with permit2 signatures as each time a stream was created a new permit2 signature was needed from the owner. Additionally any permit2 signature was short-lived due to the expiration time and typically used the exact amount needed.

Recommendation: consider using a push model rather than a pull model as the intended use case needs a preceding (approval) transaction on the token which could be replaced by a transfer() transaction. Although this doesn't solve the issue at it's core, balances are more easily to query compared to approvals (watch only address in wallets) and users are less likely to actually send more funds than needed.

[PaulRBerg]

Closing since we have decided to implement this:

#172