📝 Extended documentation for simulators (#347)

## Description

This PR updates the DDSIM documentation of all available simulators to
show more of their usage and some examples.
Interestingly, this revealed that the CoTenGra mode for the simulation
path framework was not working anymore, which was subsequently fixed.

Fixes #345 

## Checklist:

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- [x] The pull request only contains commits that are related to it.
- [x] I have added appropriate tests and documentation.
- [x] I have made sure that all CI jobs on GitHub pass.
- [x] The pull request introduces no new warnings and follows the
project's style guidelines.

.pre-commit-config.yaml

@@ -33,6 +33,11 @@ repos:
     rev: 3.2.0
     hooks:
       - id: nb-clean
+        args:
+          - --remove-empty-cells
+          - --preserve-cell-metadata
+          - raw_mimetype
+          - --
 
   # Handling unwanted unicode characters
   - repo: https://github.com/sirosen/texthooks

README.md

@@ -37,7 +37,7 @@ DDSIM bundled with the provider and backends for Qiskit is available via [PyPI](
 The following code gives an example on the usage:
 
 ```python3
-from qiskit import *
+from qiskit import QuantumCircuit
 from mqt import ddsim
 
 circ = QuantumCircuit(3)
@@ -49,7 +49,7 @@ print(circ.draw(fold=-1))
 
 backend = ddsim.DDSIMProvider().get_backend("qasm_simulator")
 
-job = execute(circ, backend, shots=10000)
+job = backend.run(circ, shots=10000)
 counts = job.result().get_counts(circ)
 print(counts)
 ```

docs/source/_static/custom.css

@@ -20,3 +20,11 @@
   align-items: center;
   justify-content: center;
 }
+
+/* override the default background color for literal strings */
+body:not([data-theme="light"]) .highlight .s1 {
+  background-color: #00000033;
+}
+body:not([data-theme="light"]) .highlight .s2 {
+  background-color: #00000033;
+}