feat: output the type of object properties in error messages

[alexander-akait]

Closes #42.

The issue asks for two things.

1. The not keyword

Already fixed on main, so this only locks the issue's three examples into snapshots:

schema	message
not: { minimum: 3 }	should be any non-number | number (should be < 3).
not: { type: "string" }	should be any non-string.
not: { enum: [1, 2] }	should not be 1 | 2.

2. The type of each property

An error listing the shape of an object gave the property names only, so it said which properties are valid but not what they take:

configuration.v should be an object:
object { foo?, bar? }

The type is now named next to the property, the form asked for in #42:

configuration.v should be an object:
object { foo?: boolean, bar?: integer }

The existing comment on that code (Maybe we should output type of property (foo: string), but it is looks very unreadable) is the real difficulty here, and it is right — naming every type unconditionally takes the longest line webpack's own schema produces from 1360 to 1959 characters. Three rules keep the output readable:

• Only a short leaf type is named. A union, an object or an array is left out; listing it inline buries the property names it sits with.
• The constraints a type carries are dropped, so number (should be >= 2) is named number — the error on the property itself states the constraint anyway.
• The types are dropped entirely once the shape no longer fits in a line. An object with that many properties is hard enough to read by the names alone. Breaking such an object over several lines is the separate issue noted in improve error reporting in some cases #42 (comment), and this leaves it untouched.

Effect on webpack

Validated against webpack's own schemas/WebpackOptions.json over a spread of invalid configurations. Exactly one line of the resulting messages changes, and it gets better:

-      [object { alias, name, onlyModule? }, ...]
+      [object { alias, name: string, onlyModule?: boolean }, ...]

Total output goes from 11024 to 11041 characters and the longest line is unchanged at 1360 — the big objects (stats, resolve, entry) render byte for byte as before.

Tests

Four cases in test/api.test.js covering the issue's example, composite types being left out, the width cap, and the three not examples. 22 existing snapshots move, each towards more information on a line no longer than before, e.g. object { apply: function, … } and object { foo?: string, bar?: number }.

npm test (490 tests, 338 snapshots), npm run lint and npm run build all pass.

🤖 Generated with Claude Code

https://claude.ai/code/session_013wqLmVHkAGBsWQgXknEQCK

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Generated by Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.66%. Comparing base (49bb7ce) to head (6767a1a).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #224      +/-   ##
==========================================
+ Coverage   95.96%   96.66%   +0.69%     
==========================================
  Files           9        9              
  Lines         967      989      +22     
  Branches      393      408      +15     
==========================================
+ Hits          928      956      +28     
+ Misses         35       31       -4     
+ Partials        4        2       -2     

Flag	Coverage Δ
integration	96.66% <100.00%> (+0.69%)	⬆️

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