Disallow untyped defs in synapse._scripts (#12422)

Of note: 

* No untyped defs in `register_new_matrix_user`

This one might be contraversial. `request_registration` has three
dependency-injection arguments used for testing. I'm removing the
injection of the `requests` module and using `unitest.mock.patch` in the
test cases instead.

Doing `reveal_type(requests)` and `reveal_type(requests.get)` before the
change:

```
synapse/_scripts/register_new_matrix_user.py:45: note: Revealed type is "Any"
synapse/_scripts/register_new_matrix_user.py:46: note: Revealed type is "Any"
```

And after:

```
synapse/_scripts/register_new_matrix_user.py:44: note: Revealed type is "types.ModuleType"
synapse/_scripts/register_new_matrix_user.py:45: note: Revealed type is "def (url: Union[builtins.str, builtins.bytes], params: Union[Union[_typeshed.SupportsItems[Union[builtins.str, builtins.bytes, builtins.int, builtins.float], Union[builtins.str, builtins.bytes, builtins.int, builtins.float, typing.Iterable[Union[builtins.str, builtins.bytes, builtins.int, builtins.float]], None]], Tuple[Union[builtins.str, builtins.bytes, builtins.int, builtins.float], Union[builtins.str, builtins.bytes, builtins.int, builtins.float, typing.Iterable[Union[builtins.str, builtins.bytes, builtins.int, builtins.float]], None]], typing.Iterable[Tuple[Union[builtins.str, builtins.bytes, builtins.int, builtins.float], Union[builtins.str, builtins.bytes, builtins.int, builtins.float, typing.Iterable[Union[builtins.str, builtins.bytes, builtins.int, builtins.float]], None]]], builtins.str, builtins.bytes], None] =, data: Union[Any, None] =, headers: Union[Any, None] =, cookies: Union[Any, None] =, files: Union[Any, None] =, auth: Union[Any, None] =, timeout: Union[Any, None] =, allow_redirects: builtins.bool =, proxies: Union[Any, None] =, hooks: Union[Any, None] =, stream: Union[Any, None] =, verify: Union[Any, None] =, cert: Union[Any, None] =, json: Union[Any, None] =) -> requests.models.Response"
```

* Drive-by comment in `synapse.storage.types`

* No untyped defs in `synapse_port_db`

This was by far the most painful. I'm happy to break this up into
smaller pieces for review if it's not managable as-is.

1 files changed, 5 insertions, 6 deletions

diff --git a/synapse/_scripts/export_signing_key.py b/synapse/_scripts/export_signing_key.py

index 66481533e9..12c890bdbd 100755
--- a/synapse/_scripts/export_signing_key.py
+++ b/synapse/_scripts/export_signing_key.py
@@ -15,19 +15,19 @@
 import argparse
 import sys
 import time
-from typing import Optional
+from typing import NoReturn, Optional
 
 from signedjson.key import encode_verify_key_base64, get_verify_key, read_signing_keys
 from signedjson.types import VerifyKey
 
 
-def exit(status: int = 0, message: Optional[str] = None):
+def exit(status: int = 0, message: Optional[str] = None) -> NoReturn:
     if message:
         print(message, file=sys.stderr)
     sys.exit(status)
 
 
-def format_plain(public_key: VerifyKey):
+def format_plain(public_key: VerifyKey) -> None:
     print(
         "%s:%s %s"
         % (
@@ -38,7 +38,7 @@ def format_plain(public_key: VerifyKey):
     )
 
 
-def format_for_config(public_key: VerifyKey, expiry_ts: int):
+def format_for_config(public_key: VerifyKey, expiry_ts: int) -> None:
     print(
         '  "%s:%s": { key: "%s", expired_ts: %i }'
         % (
@@ -50,7 +50,7 @@ def format_for_config(public_key: VerifyKey, expiry_ts: int):
     )
 
 
-def main():
+def main() -> None:
     parser = argparse.ArgumentParser()
 
     parser.add_argument(
@@ -94,7 +94,6 @@ def main():
                 message="Error reading key from file %s: %s %s"
                 % (file.name, type(e), e),
             )
-            res = []
         for key in res:
             formatter(get_verify_key(key))