fix(deps): drop runtime type-plus, inline its merge helpers

[unional]

Part of the type-plus 8.0.0 sweep.

• type-plus 8.0.0 is ESM only, and progress-str publishes a CJS build that require()d it at runtime (engines.node: ">= 20"). The build now inlines required/requiredDeep and the RecursivePartial type (ts/required.ts, fully covered by tests), and type-plus is removed from dependencies.
• Owned dev deps bumped: assertron ^11.7.1, @repobuddy/biome ^2.5.1.
• Patch changeset for progress-str.

pnpm verify passes locally (100% coverage).

🤖 Generated with Claude Code

[changeset-bot]

🦋 Changeset detected

Latest commit: 82968c7

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

This PR includes changesets to release 1 package

Name	Type
progress-str	Patch

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.20%. Comparing base (f8cdcb8) to head (82968c7).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #210      +/-   ##
==========================================
+ Coverage   99.15%   99.20%   +0.04%     
==========================================
  Files           9       10       +1     
  Lines         118      125       +7     
  Branches       44       46       +2     
==========================================
+ Hits          117      124       +7     
  Partials        1        1              

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