SOR: Confirm ERC4626/Buffers use correct rate

[johngrantuk]

Previous assumption was that token price rate could be used as rate for buffer wrap/unwrap but this isn't always the case.
Instead we should use the wrap/unwrap rate from the ERC4626 instead using convertToAssets.

See Gnosis pool as an example:
Rate provider, 0x30eacec6bd250589043de026e45dc9a158c65a1f, uses a multiplicative rate to capture all yield.
{
"id": "0x272d6be442e30d7c87390edeb9b96f1e84cecd8d",
"type": "WEIGHTED",
"poolTokens": [
{
"isErc4626": true,
"address": "0x773cda0cade2a3d86e6d4e30699d40bb95174ff2",
"symbol": "waGnowstETH",
"priceRateProvider": "0x30eacec6bd250589043de026e45dc9a158c65a1f",
"underlyingToken": {
"symbol": "wstETH",
"isErc4626": false,
"address": "0x6c76971f98945ae98dd7d4dfca8711ebea946ea6"
}
},
{
"isErc4626": true,
"address": "0x7c16f0185a26db0ae7a9377f23bc18ea7ce5d644",
"symbol": "waGnoGNO",
"priceRateProvider": "0xbbb4966335677ea24f7b86dc19a423412390e1fb",
"underlyingToken": {
"symbol": "GNO",
"isErc4626": false,
"address": "0x9c58bacc331c9aa871afd802db6379a98e80cedb"
}
}
]
},