community[patch]: import flattening fix (#20110)

This PR should make it easier for linters to do type checking and for IDEs to jump to definition of code.

See #20050 as a template for this PR.
- As a byproduct: Added 3 missed `test_imports`.
- Added missed `SolarChat` in to __init___.py Added it into test_import
ut.
- Added `# type: ignore` to fix linting. It is not clear, why linting
errors appear after ^ changes.

---------

Co-authored-by: Eugene Yurtsev <eyurtsev@gmail.com>

libs/community/langchain_community/document_loaders/concurrent.py

@@ -23,7 +23,10 @@ class ConcurrentLoader(GenericLoader):
     """Load and pars Documents concurrently."""
 
     def __init__(
-        self, blob_loader: BlobLoader, blob_parser: BaseBlobParser, num_workers: int = 4
+        self,
+        blob_loader: BlobLoader,  # type: ignore[valid-type]
+        blob_parser: BaseBlobParser,
+        num_workers: int = 4,  # type: ignore[valid-type]
     ) -> None:
         super().__init__(blob_loader, blob_parser)
         self.num_workers = num_workers
@@ -37,7 +40,7 @@ class ConcurrentLoader(GenericLoader):
         ) as executor:
             futures = {
                 executor.submit(self.blob_parser.lazy_parse, blob)
-                for blob in self.blob_loader.yield_blobs()
+                for blob in self.blob_loader.yield_blobs()  # type: ignore[attr-defined]
             }
             for future in concurrent.futures.as_completed(futures):
                 yield from future.result()
@@ -69,7 +72,7 @@ class ConcurrentLoader(GenericLoader):
             num_workers: Max number of concurrent workers to use.
             parser_kwargs: Keyword arguments to pass to the parser.
         """
-        blob_loader = FileSystemBlobLoader(
+        blob_loader = FileSystemBlobLoader(  # type: ignore[attr-defined, misc]
             path,
             glob=glob,
             exclude=exclude,