Update Cdr.cpp: fix -Wconversion warning in options_[1] assignment

[rener2020]

fix(Cdr): silence -Wconversion warning when updating options_[1]

Explicitly cast arithmetic expression to uint8_t to prevent narrowing conversion warning in GCC/Clang:

warning: conversion from ‘int’ to ‘std::array<unsigned char, 2>::value_type’ may change value [-Wconversion]

The new expression keeps the same semantics while ensuring type safety:

options_[1] = static_cast<uint8_t>(
    static_cast<uint8_t>(options_[1] & 0xC) +
    static_cast<uint8_t>(alignment & 0x3)
);

No behavioral change intended.

Description

Contributor Checklist

• Commit messages follow the project guidelines.
• The code follows the style guidelines of this project.
• Tests that thoroughly check the new feature have been added/Regression tests checking the bug and its fix have been added; the added tests pass locally
• Any new/modified methods have been properly documented using Doxygen.
• Changes are backport compatible: they do NOT break ABI nor change library core behavior.
• Changes are API compatible.
• New feature has been added to the versions.md file (if applicable).
• Applicable backports have been included in the description.

Reviewer Checklist

• The PR has a milestone assigned.
• The title and description correctly express the PR's purpose.
• Check contributor checklist is correct.
• Check CI results: changes do not issue any warning.
• Check CI results: CI pass and failing tests are unrelated with the changes.

[rener2020]

@richiprosima @rsanchez15 @richiware @depink5