feat: add framework-neutral storage core

[kauandotnet]

Summary

• add a Nest-free @nestm/storage/core export for shared storage primitives
• make Nest framework peers optional for core-only consumers
• verify the packed ESM package from a strict Node 24/TypeScript 6 consumer without Nest installed

Validation

• pnpm check
• pnpm test
• pnpm verify:pack
• git diff --check