Add row order preservation in findByIds

[goldenice]

Merge #6 and #7 first

[Copilot]

Pull Request Overview

This PR adds row order preservation to the findByIds function, ensuring returned entities maintain the same order as the input IDs array. Additionally, it refactors type definitions into separate files and introduces explicit nullability settings using 'NULLABLE' and 'NOT NULL' string literals instead of boolean values.

Key Changes

• Modified findByIds to preserve input ID ordering and handle duplicate IDs
• Refactored type definitions from main.ts into dedicated type files
• Introduced explicit nullability with 'NULLABLE'/'NOT NULL' string literals as an alternative to boolean values

Reviewed Changes

Copilot reviewed 20 out of 23 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
tests/pg-backend/findByIds.test.ts	Added tests for ID order preservation including ascending, descending, and duplicate ID scenarios
src/main.ts	Refactored findByIds to preserve input order, renamed prepEntity to createOutputTypeFromRawSqlType, updated nullability checks
src/entities/BaseEntity.ts	Updated field and relation definitions to use new Nullable type
src/entities/Nullable.ts	New file defining Nullable type and isNullable helper function
src/types/*.ts	New type definition files extracted from main.ts
src/helpers/sql.ts	Moved mergeSql function from main.ts
src/relations/ormRelationGetter.ts	Extracted relation getter logic into separate file
src/tools/validateSchema.ts	Updated import paths
tests/testHelpers.ts	Updated import for isOrmRelationGetter
eslint.config.js	Commented out require-atomic-updates rule
.changeset/fair-knives-notice.md	Added changeset for nullability feature

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