fix(type-plus)!: let a later stub.builder().with() object win

[unional]

Summary

• stub.builder({ a: 1 }).with({ a: 5 }).create()() returned { a: 1 }: a later .with() object only filled keys the earlier initializers left unset. It now returns { a: 5 }.
• Precedence, now stated in the TSDoc and on the website:
  • An object initializer is deep-merged over the earlier ones, so a later .with() value wins. Nested keys it does not set are kept.
  • The partial stub passed to the call wins over every object initializer.
  • A function initializer receives the stub so far (the call-time stub merged with the initializers before it) and returns the next stub, used as is. It can override call-time values if it chooses, which keeps the existing stub.build((s) => ({ a: (s?.a ?? 0) + 1 })) behavior.
• Implementation: each object initializer is merged over the accumulator with the paths the call-time stub sets stripped out, so a later object never overrides a call-time value, and never undoes a value an earlier function returned for a key it does not set.
• Documented @examples are pinned in stub.builder.spec.ts / stub.build.spec.ts.
• Includes the earlier commit giving stub.build and stub.builder their own website sections.
• Changeset: type-plus major (8.0 is unreleased).

Verification

• pnpm verify passes, including type tests on TS 5.4, 5.5, 5.6, 6.0 and 7, and the error snapshots.

🤖 Generated with Claude Code

[changeset-bot]

🦋 Changeset detected

Latest commit: ae0797e

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
type-plus	Major

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (9b2b94c) to head (ae0797e).

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #821   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files           40        40           
  Lines          173       182    +9     
  Branches        30        35    +5     
=========================================
+ Hits           173       182    +9     

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