feat(deepMerge): only merge plain objects

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commit: 12c5bf3

[Copilot]

Pull request overview

This PR modifies the deepMerge function to only deeply merge plain objects (object literals), while treating built-in objects like Date, Map, Set, and RegExp as atomic values that should be replaced rather than merged.

Key changes:

• Introduced a new isPlainObject helper function that distinguishes plain objects from built-in objects and class instances
• Updated deepMerge to use isPlainObject instead of isObject for merge decisions
• Added comprehensive test coverage for the new behavior with various built-in object types

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
packages/helpers/src/is.js	Added new isPlainObject function to check if a value is a plain object literal
packages/helpers/src/is.test.js	Added comprehensive tests for isPlainObject covering primitives, arrays, built-in objects, and custom prototypes
packages/helpers/src/merge.js	Updated deepMerge to use isPlainObject instead of isObject to prevent merging built-in objects
packages/helpers/src/merge.test.js	Added tests verifying that RegExp, Map, Set, and Date objects are replaced rather than merged

Comments suppressed due to low confidence (1)

packages/helpers/src/merge.js:7

• The function documentation should be updated to clarify that it only deeply merges plain objects (object literals). Built-in objects like Date, Map, Set, and RegExp are replaced rather than merged. Consider updating the JSDoc to explain this behavior, for example: "Deeply merges two plain objects. Built-in objects (Date, Map, Set, RegExp, etc.) are replaced by the source value rather than merged."

/**
 * Deeply merges two objects.
 * @param {*} target - The target object to merge into.
 * @param {*} source - The source object to merge from.
 * @returns {*} - The merged object.

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