(2/2) Combine Pauli measurements and postselection (#7970)

This commit implements the postselection symmetry functionality in
`CircuitToPauliStringsParameters`. Circuits provided with
`postselection_symmetries` will now successfully filter measurement
results based on the expected eigenvalues rather than defaulting to the
confusion matrix method.

---------

Co-authored-by: Pavol Juhas <juhas@google.com>

Author: ddddddanni

cirq-core/cirq/contrib/paulistring/__init__.py

@@ -46,4 +46,5 @@
 from cirq.contrib.paulistring.pauli_string_measurement_with_readout_mitigation import (
     measure_pauli_strings as measure_pauli_strings,
     CircuitToPauliStringsParameters as CircuitToPauliStringsParameters,
+    CircuitToPauliStringsMeasurementResult as CircuitToPauliStringsMeasurementResult,
 )