feat(cpp): Add bazel + cmake building and testing infrastructure

[slbotbm]

Which issue does this PR close?

Closes #2762

Rationale

What changed?

Adds bazel + cmake build systems for C++. Defines some stub classes in include/iggy.hpp and tests those using googletest. See README.md for execution instructions.

TODO: CI scripts

Local Execution

• Passed
• Pre-commit hooks ran

AI Usage

If AI tools were used, please answer:

1. Which tools? OpenAI codex
2. Scope of usage? used for creating the build system.
3. How did you verify the generated code works correctly? ran all commands and tests locally.
4. Can you explain every line of the code if asked? I can explain about 80% (Some parts of the build system are difficult to understand)

[slbotbm]

With regards to the CI, should I build and test using both cmake and bazel, or with either one of the two?