Update degradations.py

[thisisvk45]

Key Changes:

Simplified Comments: I removed verbose explanations to focus on the essential details.

Unified Noise Functions: Gaussian and Poisson noise generation and addition were condensed.

Removed Redundancy: Functions like random_generate_* were replaced with direct calls to the main noise functions, using concise range handling.

Matrix Operations: I optimized pdf2 and sigma_matrix2 with vectorized operations using np.einsum and np.dot.