Dazl

python: No longer retry ACS fetches from a closed connection (250), as those will always fail.

python:
* Fix minor typing issues in dazl.ledgerutil.ACS.
* Add `dazl.ledgerutil.fetch_first` and `dazl.ledgerutil.fetch_last` functions.

Minor bug fix to an internal serialization routine.

Introduce a new API, ``dazl.connect``, that is much lighterweight and stateless than ``dazl.Network``.

See the migration guide (https://digital-asset.github.io/dazl-client/migrating.html) for changes that were made as part of this release. Note that the ``dazl.Network`` API continues to work, and will be available for the foreseeable future; you are encouraged, however, to try out the new API for new projects.

Example

py
import dazl

async with dazl.connect(url='http://localhost:6865', act_as='Alice') as conn:
await conn.create('Main:Asset', {'issuer': 'Alice', 'owner': 'Alice', 'name': 'hello world!'})

python:
* Fix a bug where trying to read from the ACS with a fully-qualified template name that had no contracts would result in an error instead of an empty collection.
* Dramatically reduce the number of warnings emitted when using Daml-LF 1.11 DARs.

*NOTE:*
dazl 8 (the _next_ major version of dazl) will require Python 3.8 or newer! You should upgrade your Python environment accordingly.

python: Fix an error in the way that `dazl` referred to typing rules that made dazl inadvertently incompatible with Python 3.7. (Python 3.6 and Python 3.8+ or later are unaffected.)