fix(build): remove sandbox-dependent generated overlay paths

[mstykow]

Summary

• move the shared build version formatter out of src/ into build_support/ so build-only shared code does not masquerade as a runtime module
• include build_support/**/* in packaged sources so crates.io source builds still contain the shared helper
• generate bundled overlay manifests with inlined string contents instead of include_str! absolute paths so Cargo and Buck builds do not depend on matching rustc/build-script sandboxes

Scope and exclusions

• Included: build script portability fixes, shared helper relocation, and source-package include list updates
• Explicit exclusions: no runtime license overlay semantics changes, no overlay fixture content changes, and no Buck-specific repository wiring beyond removing the sandbox path dependency

Follow-up work

• Created or intentionally deferred: CI or Buck-native validation can now verify the sandbox-safe manifest generation on the downstream integration side