Prototype immutable path writer

[hatim-s]

Feature

Replace Bolt nested-path writes with a custom immutable writer that clones only the root and changed path ancestors. This keeps the public API and React snapshot semantics unchanged while removing Mutative from the hot nested-write path.

Architecture

Before:

set(path, value)
  -> Mutative draft
  -> lodash/set on draft
  -> finalized immutable state
  -> notify root + path prefixes

After:

set(path, value)
  -> read previous leaf
  -> compute next leaf
  -> Object.is no-op short-circuit
  -> clone root + path ancestors only
  -> assign leaf
  -> notify root + path prefixes

Notes

• Root replacement remains direct assignment.
• Parent/root subscribers still receive changed object references.
• Sibling references are preserved.
• Missing numeric branches still create arrays.
• Mutative dependency and library external config are removed.

Validation

• bun run test
• bun run build:lib
• bun run build