[decimal] Update Decimal constructors

[forfudan]

This pull request includes several changes to the DeciMojo library to simplify the initialization of Decimal objects and improve code readability.

Codebase Simplification:

• Removed the from_words method and replaced its usage with direct calls to the Decimal constructor.
• Added a new constructor to initialize Decimal objects with four raw words and another constructor to initialize Decimal objects with five components.

Testing:

• Imported the testing module to add assertions for validating the flags word in the new constructor.
• Updated test cases to use the new Decimal constructor instead of from_words.