feat: Add ifError assertion for Node.js error handling

[nev21]

Add assert.ifError() and expect().to.ifError() assertions for Node.js-style callback error checking. Passes for falsy values, throws Error instances, and fails for truthy non-Error values.

Includes comprehensive tests (35 cases), chai shim integration, and full documentation updates.

[Copilot]

Pull request overview

This PR adds the ifError() assertion for Node.js-style callback error handling. The implementation follows Node.js's assert.ifError() behavior: it passes for falsy values, throws Error instances directly, and fails with an AssertionFailure for truthy non-Error values.

Changes:

• Added ifError() assertion to both assert and expect APIs
• Integrated Chai.js compatibility shim support for ifError()
• Added comprehensive test coverage with 35 test cases covering falsy values, Error instances, truthy non-Error values, custom messages, edge cases, and typical use patterns

Reviewed changes

Copilot reviewed 10 out of 12 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
core/src/assert/funcs/ifError.ts	Core implementation of ifError assertion function
core/src/assert/assertClass.ts	Integration of ifError into assert class
core/src/assert/interface/IAssertClass.ts	TypeScript interface definition for assert.ifError()
core/src/assert/interface/ops/IToOp.ts	TypeScript interface definition for expect().to.ifError()
core/src/assert/ops/toOp.ts	Integration of ifError into expect chain
core/test/src/assert/assert.ifError.test.ts	Comprehensive test suite with 35 test cases
shim/chai/src/assert/chaiAssert.ts	Chai compatibility shim integration
shim/chai/test/src/chaiAssert.test.ts	Chai compatibility test
core/README.md	Documentation update listing ifError in features
shim/chai/README.md	Documentation update listing ifError in implemented features
core/src/assert/funcs/keysFunc.ts	Whitespace cleanup (removing trailing spaces from comments)
core/src/assert/ops/keysOp.ts	Whitespace cleanup (removing trailing spaces from comments)