feat: added sam_flag module

[rLannes]

Description:

This pull request introduces a new module, bam::sam_flag, to facilitate easier handling of SAM flags. The module provides a more intuitive and type-safe way to work with SAM flags, improving code readability and reducing potential errors.

Key features:

1. SamFlag struct: A zero-cost abstraction that contains constants for all standard SAM flags.
2. check_flag() function: A utility function to easily check for the presence or absence of specific flags.

Benefits:

• Improved code readability when working with SAM flags.
• Reduced chance of errors from manual flag manipulation.
• Type-safe constants for all standard SAM flags.
• Easy-to-use function for checking flag combinations.

Implementation choice:
The main design choice was to use a struct with associated constants rather than an enum to represent the flag values. The benefit is no runtime cost, but it comes at the cost of not being as nice to work with as an enum.

Example usage:

let read_flag = 65; // PAIRED (1) + FIRST_IN_PAIR (64)
assert!(check_flag(read_flag, SamFlag::PAIRED + SamFlag::FIRST_IN_PAIR, SamFlag::READ_UNMAPPED));