Type some methods in noise_model.py

[vtomole]

Part of #4393

[vtomole]

Checks are failing due to flakes.

[95-martin-orion]

Checks are failing due to flakes.

Re-triggered the tests to get a green run.

[CirqBot]

Automerge cancelled: A required status check is not present.

Missing statuses: ['Coverage check', 'Pytest Windows (3.7)', 'Pytest Windows (3.8)', 'Pytest Windows (3.9)', 'Typescript lint check', 'Typescript tests', 'Typescript tests coverage']

[CirqBot]

Automerge cancelled: A required status check is not present.

Missing statuses: ['Typescript lint check', 'Typescript tests', 'Typescript tests coverage']

[CirqBot]

Automerge cancelled: A required status check is not present.

Missing statuses: ['Build docs', 'Build protos', 'Changed files test', 'Coverage check', 'Doc test', 'Format check', 'Lint check', 'Misc check', 'Notebook formatting', 'Pytest MacOS (3.7)', 'Pytest MacOS (3.8)', 'Pytest MacOS (3.9)', 'Pytest Ubuntu (3.7)', 'Pytest Ubuntu (3.8)', 'Pytest Ubuntu (3.9)', 'Pytest Windows (3.7)', 'Pytest Windows (3.8)', 'Pytest Windows (3.9)', 'Type check', 'Typescript lint check', 'Typescript tests', 'Typescript tests coverage']