Switch models to safir.github

Use safir.github.webhooks for webhook payloads and safir.github.models
for the GitHub REST API resources. The githubcheckrun, githubcheckout,
and githubtree models persist because they reflect internal models
(but they're related to github concepts)

src/timessquare/domain/githubcheckout.py

@@ -12,8 +12,8 @@
 import yaml
 from gidgethub.httpx import GitHubAPI
 from pydantic import BaseModel, EmailStr, Field, HttpUrl, root_validator
+from safir.github.models import GitHubBlobModel, GitHubRepositoryModel
 
-from .githubapi import GitHubBlobModel, GitHubRepositoryModel
 from .page import PageParameterSchema, PersonModel
 
 

src/timessquare/domain/githubcheckrun.py

@@ -9,17 +9,17 @@
 
 from gidgethub.httpx import GitHubAPI
 from pydantic import ValidationError
-
-from timessquare.config import config
-
-from .githubapi import (
+from safir.github.models import (
     GitHubBlobModel,
     GitHubCheckRunAnnotationLevel,
     GitHubCheckRunConclusion,
     GitHubCheckRunModel,
     GitHubCheckRunStatus,
     GitHubRepositoryModel,
 )
+
+from timessquare.config import config
+
 from .githubcheckout import (
     GitHubRepositoryCheckout,
     NotebookSidecarFile,