fix: Can't record mock files when using parallel processing

[MMenchero]

Description

The nixtlar package currently includes both sequential and parallel versions of its main methods due to issues with parallel processing that prevent the recording of mock files needed for vignette creation.

Problem:
Having two versions of each method can result in inefficiencies and is more difficult to maintain.

Proposed Solution:
Ideally, we should find a way to handle parallel processing that still records mock files with the httptest2 successfully, or reconsider the architecture to minimize the need for dual versions.

Methods affected

• forecast
• historic
• cross_validation
• detect_anomalies