Remove schematype caster and casterConstructor properties in favor of embeddedSchemaType and Constructor

[vkarpov15]

Summary

#15179 is a result of an issue that's frustrated me for several years: inconsistency in the caster and casterConstructor properties. In Mongoose 8, caster can be either a schema type instance or an embedded document constructor depending on document array vs primitive array, which is inconsistent and confusing. With this PR, we split it up into:

1. embeddedSchemaType now stores the embedded schema type for arrays and document arrays. Likely should consider switching maps too, but maps for now use $__schemaType.
2. Constructor now stores the embedded document constructor for subdocuments and document arrays.

This should improve internal maintainability, and make our TypeScript types more coherent. However, this will also unfortunately break anyone's code that relies on caster, which is why we're putting this in Mongoose 9.

Examples

[Copilot]

Pull Request Overview

This PR refactors array and subdocument schema types by removing the old caster/casterConstructor properties and replacing them with embeddedSchemaType and Constructor, simplifying internal logic and improving TypeScript types.

• Replace path.caster.instance checks and uses with path.embeddedSchemaType.instance
• Migrate all casterConstructor references to the new Constructor property
• Update tests and documentation to reflect the new property names

Reviewed Changes

Copilot reviewed 31 out of 32 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
test/schema.test.js	Updated assertions from caster/casterConstructor to embeddedSchemaType/Constructor
test/schema.documentarray.test.js	Switched .$embeddedSchemaType to .embeddedSchemaType
test/query.test.js	Replaced .caster with .Constructor for bookHolder path
test/document.test.js	Updated path.casterConstructor to path.Constructor
package.json	Contains unresolved merge conflict markers
lib/types/documentArray/methods/...	Replaced casterConstructor with Constructor in methods
lib/types/documentArray/index.js	Updated internal array schema symbol to use embeddedSchemaType
lib/types/array/methods/index.js	Redirected setter/getter calls from caster to embeddedSchemaType
lib/types/array/index.js	Switched getter logic to use embeddedSchemaType
lib/schemaType.js	Updated getEmbeddedSchemaType to return this.embeddedSchemaType
lib/schema/subdocument.js	Removed this.caster, added this.Constructor assignments
lib/schema/documentArrayElement.js	Changed constructor signature to (path, schema, options)
lib/schema/documentArray.js	Reworked document array initialization to use embeddedSchemaType and Constructor
lib/schema/array.js	Refactored SchemaArray to set embeddedSchemaType
lib/schema.js	Updated childSchemas logic to reference Constructor and embeddedSchemaType
lib/helpers/...	Various query, populate, plugin helpers updated from caster/casterConstructor to new properties
docs/migrating_to_9.md	Added migration guide for caster → embeddedSchemaType and Constructor

Comments suppressed due to low confidence (2)

package.json:57

• Resolve the Git merge conflict markers by removing <<<<<<<, =======, and >>>>>>> and consolidating the correct dependency versions under a single block.

    "pug": "3.0.3",

lib/schema/documentArrayElement.js:21

• [nitpick] Update the JSDoc or add parameter comments to document the newly introduced schema parameter for SchemaDocumentArrayElement.

function SchemaDocumentArrayElement(path, schema, options) {