Sync support

[anand2312]

This PR adds:

• sync/async support with unasync and httpx, as implemented in postgrest-py
• File API actions can now be used on Bucket objects as well
  Example:

from storage3 import create_client

client = create_client(url, headers, is_async=False)
client.from_("test").list()  # lists files in `test` bucket

bucket = client.get_bucket("test")
# an instance of SyncBucket/AsyncBucket
bucket.list()  # works just like client.from_().list()

[anand2312]

@J0 @leynier could you give this a review when you can? 😄