RFC: Rewriting core base library and XDR usage library in TypeScript (proposal + review)

[sagpatil]

Motivation: A full TypeScript rewrite may yield long-term benefits for type safety and DX but requires careful planning.

Proposed approach:

• Publish an RFC describing scope, migration strategy (staged migration, dual-publishing), compatibility concerns, and risk mitigation.
• Collect feedback from maintainers and major consumers; run a small pilot if the RFC is approved.

Acceptance criteria:

• RFC published and reviewed; a decision or roadmap is recorded.

[sagpatil]

Parent epic: #1243