Improved pipeline validation

[snopoke]

Description

Improve pipeline validation to try and reduce the likelyhood of creating invalid pipelines like this one:

There is an issue with the UI updating (auto-save doesn't update the node / edge data) which I still need to resolve but I'll do that in a separate PR since this one is big enough.

User Impact

Better pipeline validation and error display.

Demo

[codecov-commenter]

❌ 2 Tests Failed:

Tests completed	Failed	Passed	Skipped
820	2	818	0

View the top 2 failed tests by shortest run time

apps/pipelines/tests/test_runnable_builder.py::test_cyclical_graph

Stack Traces | 1.17s run time

.../pipelines/tests/test_runnable_builder.py:735: in test_cyclical_graph
    create_runnable(pipeline, nodes, edges)
.../pipelines/tests/utils.py:32: in create_runnable
    return PipelineGraph.build_runnable_from_pipeline(pipeline)
apps/pipelines/graph.py:89: in build_runnable_from_pipeline
    return cls.build_from_pipeline(pipeline).build_runnable()
apps/pipelines/graph.py:107: in build_runnable
    self._validate_no_parallel_nodes()
apps/pipelines/graph.py:138: in _validate_no_parallel_nodes
    raise PipelineBuildError(
E   apps.pipelines.exceptions.PipelineBuildError: Multiple edges connected to the same output

During handling of the above exception, another exception occurred:
.../pipelines/tests/test_runnable_builder.py:734: in test_cyclical_graph
    with pytest.raises(PipelineBuildError, match="A cycle was detected"):
E   AssertionError: Regex pattern did not match.
E    Regex: 'A cycle was detected'
E    Input: 'Multiple edges connected to the same output'

apps/pipelines/tests/test_runnable_builder.py::test_branching_pipeline

Stack Traces | 2.22s run time

.../pipelines/tests/test_runnable_builder.py:221: in test_branching_pipeline
    output = create_runnable(pipeline, nodes, edges).invoke(
.../pipelines/tests/utils.py:32: in create_runnable
    return PipelineGraph.build_runnable_from_pipeline(pipeline)
apps/pipelines/graph.py:89: in build_runnable_from_pipeline
    return cls.build_from_pipeline(pipeline).build_runnable()
apps/pipelines/graph.py:107: in build_runnable
    self._validate_no_parallel_nodes()
apps/pipelines/graph.py:138: in _validate_no_parallel_nodes
    raise PipelineBuildError(
E   apps.pipelines.exceptions.PipelineBuildError: Multiple edges connected to the same output

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[SmittieC]

Overall looks good to me