Expose tobiaslocker/base64 as an external dependency

The project currently handles tobiaslocker/base64 differently from all other third‑party dependencies. Instead of being managed as a normal external dependency, it is effectively bundled inside the repo.

This creates problems for downstream consumers, especially those using Conan, because:

• In Conan builds, it becomes a hidden/transitive dependency, the dependency becomes invisible in the dependency graph
• Inconsistency, the base64 library is not exposed in the same way as other third‑party dependencies.
• License checks and compliance workflows can’t detect it reliably.
• Consumers cannot choose their own base64 library or version, which reduces flexibility.

Proposed solution can be found in the following commit.

Start with the proposed solution in pull request 315, commit a444d26e00aa51f855d16169c58946b8cd6a73bc, and trace how tobiaslocker/base64 is currently bundled and declared. Apply the same external-dependency treatment used for the other third-party dependencies, then verify that Conan exposes base64 in the dependency graph and that compliance checks can detect it.