Add a new proto DeviceParametersDiff which provides a compact way to bundle multiple DeviceParameters and their values

[kmlau]

The new proto DeviceParametersDiff is for a user to compose a RunJobRequest for invoking RunJob rpc on a Cirq server, in particular to populate the RunJobRequest.run_context field with device parameters overrides to customize the circuit(s) execution with some control on the device's samples data.

This is based on a design reviews to add "device parameters overrides" before executing circuits sweeping.

I renamed some proto type names from similar internal data structure to prevent reference to internal infrastructures.

[kmlau]

cc @dstrain115

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 97.81%. Comparing base (6709046) to head (8e79f46).

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```diff @@ Coverage Diff @@ ## main #6583 +/- ## ======================================= Coverage 97.81% 97.81% ======================================= Files 1061 1063 +2 Lines 91455 91501 +46 ======================================= + Hits 89454 89500 +46 Misses 2001 2001 ```

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[kmlau]

How will users interact with this new proto? IIUC, the internal diff proto has an abstraction layer that clients can easily interact with for creating a Diff which can then be easily packaged into its proto form. Can a similar well defined abstraction layer e.g class DeviceParameterDiff exist for this proto as well? It doesn't have to include all the APIs as the one linked, but a clear abstraction layer will help me see how this proto will later get integrated into a Job's run context. WDYT?

thanks for the comment.

the PR includes a helper function to construct a DeviceParametersDiff proto out of a list of DeviceParameter and their values. please see the module run_context.py in this PR. Suppose you want to override some readout parameters on 2 qubits, and build a RunContext proto with such overrides, you may use the following code

import run_context

device_params_override = run_context.to_device_parameters_diff([
    (
        run_context_pb2.DeviceParameter(
            path=["q1_2", "readout_default", "readoutDemodDelay"], units="ns"
        ),
        program_pb2.ArgValue(float_value=5.0),
    ),
    (
        run_context_pb2.DeviceParameter(
            path=["q3_4", "readout_default", "readoutFidelities"]),
        program_pb2.ArgValue(
            double_values=program_pb2.RepeatedDouble(values=[0.991, 0.993])
        ),
    ),
])

my_rc = run_context_pb2.RunContext(
    device_parameters_override=device_params_override)

[kmlau]

friendly ping @senecameeks and @dstrain115