fix(zne_estrategy): update default amplifier to multi-qubit (#62)

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### Summary
Update default amplifier in `ZNEStrategy` to act on all multi-qubit
gates (i.e. `MultiQubitAmplifier`) instead of just two-qubit gates (i.e.
`TwoQubitAmplifier`).


### Details and comments
Builds towards solving #58

test/test_zne_strategy.py

@@ -22,7 +22,7 @@
 
 from zne.extrapolation import Extrapolator, LinearExtrapolator
 from zne.noise_amplification import NoiseAmplifier
-from zne.noise_amplification.folding_amplifier import TwoQubitAmplifier
+from zne.noise_amplification.folding_amplifier import MultiQubitAmplifier
 from zne.zne_strategy import ZNEStrategy
 
 from . import NO_ITERS_NONE, NO_NONE
@@ -68,7 +68,7 @@ class TestInit:
 
     def test_defaults(self):
         """Test default configuration."""
-        assert ZNEStrategy().noise_amplifier == TwoQubitAmplifier()
+        assert ZNEStrategy().noise_amplifier == MultiQubitAmplifier()
         assert ZNEStrategy().noise_factors == (1,)
         assert ZNEStrategy().extrapolator == LinearExtrapolator()
 
@@ -277,7 +277,7 @@ class TestNoiseAmplifier:
     def test_default(self):
         zne_strategy = ZNEStrategy()
         zne_strategy.noise_amplifier = None
-        assert zne_strategy.noise_amplifier == TwoQubitAmplifier()
+        assert zne_strategy.noise_amplifier == MultiQubitAmplifier()
 
     @mark.parametrize(
         "noise_amplifier",

zne/zne_strategy.py

@@ -24,7 +24,7 @@
 from qiskit.primitives import EstimatorResult
 
 from .extrapolation import Extrapolator, LinearExtrapolator
-from .noise_amplification import NoiseAmplifier, TwoQubitAmplifier
+from .noise_amplification import MultiQubitAmplifier, NoiseAmplifier
 from .types import EstimatorResultData, Metadata  # noqa: F401
 from .utils.grouping import from_common_key, group_elements_gen, merge_dicts
 from .utils.typing import isreal, normalize_array
@@ -120,7 +120,7 @@ def noise_factors(self, noise_factors: Sequence[float]) -> tuple[float, ...]:
 
         return noise_factors
 
-    @quality(default=TwoQubitAmplifier())
+    @quality(default=MultiQubitAmplifier())
     def noise_amplifier(self, noise_amplifier: NoiseAmplifier) -> NoiseAmplifier:
         """Noise amplifier strategy for ZNE.