docs(contracts): update creator -> funder in Validator interface

also add `@dev` to Validator.vyi

contracts/Validator.json

@@ -4,7 +4,7 @@
     "name": "validate",
     "stateMutability": "nonpayable",
     "inputs": [
-      { "name": "creator", "type": "address" },
+      { "name": "funder", "type": "address" },
       { "name": "token", "type": "address" },
       { "name": "amount", "type": "uint256" },
       { "name": "products", "type": "bytes32[]" }

contracts/Validator.vyi

@@ -1,5 +1,22 @@
 """
 @title StreamManager Validation Interface Specification
+@dev
+    Validators for the ApePay StreamManager are an important part of how your system can be
+    customized for the requirements of your product, organization, and operation of payments.
+    There are several use cases for a Validator, and of course any use case where you need to
+    "hook" into the pre-payment validation point can be covered.
+
+    Here are some use cases for a Validator:
+
+        1. Check if a stream funder is authorized to do so, based on a pre-vetted list
+           (see [Allowlist.vy](./validators/Allowlist.vy))
+        2. Check if a stream funder is a known bad actor, against an internal or external
+           list (see [Denylist.vy](./validators/Denylist.vy))
+        3. Check if the amount of time being funded is too large (e.g. operating a beta)
+        4. Compute the `stream_life` for a given set of products (not all validators need to)
+        5. Update and track any internal state for other purposes (airdrops, NFT mints, etc.)
+        6. Emit more logs (for other Silverback services to hook onto)
+
 @notice
     Implement this interface with any additional checks that should be performed on stream
     creation, funding or migration events in order to block certain behaviors or modify the stream
@@ -10,7 +27,7 @@ from ethereum.ercs import IERC20
 
 @external
 def validate(
-    creator: address,
+    funder: address,
     token: IERC20,
     amount: uint256,
     products: DynArray[bytes32, 20],

contracts/validators/Allowlist.vy

@@ -43,10 +43,10 @@ def deny(denied: DynArray[address, 100]):
 
 @external
 def validate(
-    creator: address,
+    funder: address,
     token: IERC20,
     amount: uint256,
     products: DynArray[bytes32, MAX_PRODUCTS],
 ) -> uint256:
-    assert self.is_allowed[creator]
+    assert self.is_allowed[funder]
     return 0  # This validator does not compute any product costs

contracts/validators/Denylist.vy

@@ -51,10 +51,10 @@ def deny(denied: DynArray[address, 100]):
 
 @external
 def validate(
-    creator: address,
+    funder: address,
     token: IERC20,
     amount: uint256,
     products: DynArray[bytes32, MAX_PRODUCTS],
 ) -> uint256:
-    assert not self.is_denied[creator]
+    assert not self.is_denied[funder]
     return 0  # This validator does not compute any product costs