build: add waves-ext project dependency to core build

[D-H-O-R-A]

This change integrates the waves-ext project dependency directly into the root Waves platform SBT build.

Key improvements:

• Declared the waves-ext lazy project, establishing explicit dependencies on the node (compile/runtime) and grpc-server modules.
• Added waves-ext to the root project's aggregate list, ensuring it compiles as part of the main Waves build and packaging flow.
• Configured proper source generators for Protobuf (scalapb.gen) under waves-ext to resolve the required schemas dynamically.
• Fixes classloader and linkage issues when loading custom dex extension modules alongside the node JVM in custom network environments.

Developer Contact:

• Email: diegoantunes2301@gmail.com
• WhatsApp: +5511974289097

[phearnot]

Thanks for your contribution.
What would be the point of a placeholder project?

[D-H-O-R-A]

It's not a placeholder. waves-ext is the DEX extension module — the full implementation is in wavesplatform/matcher#761.

Adding it to the core build ensures it compiles against the same node internals and gets included in the packaging flow, avoiding binary incompatibilities at runtime.

Check the matcher PR for context.