How many epochs does fit method run
In scikit-learn's linear regression, the parameters that minimise the squared error loss aren't estimated using gradient descent, they are computed exactly.

The minimisation problem for linear least squares is

$$
\hat{\beta} = \underset{\beta}\arg \min || \mathbf{y} - \beta \mathbf{X} ||^2
$$

which has a unique solution (assuming the columns of $\mathbf{X}$ are linearly independent):

$$
\hat{\beta} = (\mathbf{X}^\text{T}\mathbf{X})^{-1}\mathbf{X}^\text{T}\mathbf{y}
$$

For classifiers that are fitted with an iterative optimisation process like gradient descent, e.g., MLPClassifier, there is a parameter called max_iter which sets the maximum number of epochs. If tol is set to 0, the optimisation will run for max_iter epochs.