feat: add mergeSchemas function (#1)

.gitattributes

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+# Set default behavior to automatically convert line endings
+* text=auto eol=lf

.github/test.yml

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+name: Run Tests
+
+on: [push, pull_request]
+
+permissions:
+  contents: read
+
+jobs:
+  test:
+    name: Test
+    runs-on: ${{ matrix.os }}
+
+    strategy:
+      matrix:
+        node-version: [18.x, 20.x]
+        os: [ubuntu-latest, windows-latest, macOS-latest] 
+
+    steps:
+    - uses: actions/checkout@v3
+
+    - name: Use Node.js ${{ matrix.node-version }}
+      uses: actions/setup-node@v3
+      with:
+        node-version: ${{ matrix.node-version }}
+
+    - name: Install
+      run: |
+        npm install
+
+    - name: Test
+      run: |
+        npm run test

.npmrc

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+package-lock=false

README.md

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+# merge-json-schema
+
+__merge-json-schema__ is a javascript library that build a logical product (AND) for multiple [JSON schemas](https://json-schema.org/draft/2020-12/json-schema-core#name-introduction).
+
+- [Installation](#installation)
+- [Usage](#usage)
+- [API](#api)
+  - [mergeSchemas(schemas, options)](#mergeschemasschemas-options)
+  - [resolvers](#resolvers)
+  - [defaultResolver](#defaultresolver)
+- [License](#license)
+
+<a name="installation"></a>
+
+## Installation
+
+```bash
+npm install merge-json-schema
+```
+
+<a name="usage"></a>
+
+## Usage
+
+```javascript
+const assert = require('node:assert')
+const { mergeSchemas } = require('merge-json-schema')
+
+const schema1 = {
+  $id: 'schema1',
+  type: 'object',
+  properties: {
+    foo: { type: 'string', enum: ['foo1', 'foo2'] },
+    bar: { type: 'string', minLength: 3 }
+  }
+}
+
+const schema2 = {
+  $id: 'schema1',
+  type: 'object',
+  properties: {
+    foo: { type: 'string', enum: ['foo1', 'foo3'] },
+    bar: { type: 'string', minLength: 5 }
+  },
+  required: ['foo']
+}
+
+const mergedSchema = mergeSchemas([schema1, schema2])
+assert.deepStrictEqual(mergedSchema, {
+  $id: 'schema1',
+  type: 'object',
+  properties: {
+    foo: { type: 'string', enum: ['foo1'] },
+    bar: { type: 'string', minLength: 5 }
+  },
+  required: ['foo']
+})
+```
+
+<a name="api"></a>
+
+## API
+
+<a name="merge-schemas"></a>
+
+#### mergeSchemas(schemas, options)
+
+Builds a logical conjunction (AND) of multiple [JSON schemas](https://json-schema.org/draft/2020-12/json-schema-core#name-introduction).
+
+- `schemas` __\<objects[]\>__ - list of JSON schemas to merge.
+- `options` __\<object\>__ - optional options.
+  - `resolvers` __\<object\>__ - custom resolvers for JSON schema keywords. Each key is the name of a JSON schema keyword. Each value is a resolver function. See [keywordResolver](#keywordresolver-keyword-values-mergedschema-parentschemas-options).
+  - `defaultResolver` __\<function\>__ - custom default resolver for JSON schema keywords. See [keywordResolver](#keywordresolver-keyword-values-mergedschema-parentschemas-options).
+  - `onConflict` __\<string\>__ - action to take when a conflict is found. Used by the default `defaultResolver`. Default is `throw`. Possible values are:
+    - `throw` - throws an error if found a multiple different schemas for the same keyword.
+    - `ignore` - do nothing if found a multiple different schemas for the same keyword.
+    - `first` - use the value of the first schema if found a multiple different schemas for the same keyword.
+
+#### resolvers
+
+A list of default resolvers that __merge-json-schema__ uses to merge JSON schemas. You can override the default resolvers by passing a list of custom resolvers in the `options` argument of `mergeSchemas`. See [keywordResolver](#keywordresolver-keyword-values-mergedschema-parentschemas-options).
+
+#### defaultResolver
+
+A default resolver that __merge-json-schema__ uses to merge JSON schemas. Default resolver is used when no custom resolver is defined for a JSON schema keyword. By default, the default resolver works as follows:
+
+- If only one schema contains the keyword, the value of the keyword is used as the merged value.
+- If multiple schemas contain the exact same value for the keyword, the value of the keyword is used as the merged value.
+- If multiple schemas contain different values for the keyword, it throws an error.
+
+#### keywordResolver (keyword, values, mergedSchema, parentSchemas, options)
+
+__merge-json-schema__ uses a set of resolvers to merge JSON schemas. Each resolver is associated with a JSON schema keyword. The resolver is called when the keyword is found in the schemas to merge. The resolver is called with the following arguments:
+
+- `keyword` __\<string\>__ - the name of the keyword to merge.
+- `values` __\<any[]\>__ - the values of the keyword to merge. The length of the array is equal to the number of schemas to merge. If a schema does not contain the keyword, the value is `undefined`.
+- `mergedSchema` __\<object\>__ - an instance of the merged schema.
+- `parentSchemas` __\<object[]\>__ - the list of parent schemas.
+- `options` __\<object\>__ - the options passed to `mergeSchemas`.
+
+The resolver must set the merged value of the `keyword` in the `mergedSchema` object.
+
+__Example:__ resolver for the `minNumber` keyword.
+
+```javascript
+function minNumberResolver (keyword, values, mergedSchema) {
+  mergedSchema[keyword] = Math.min(...values)
+}
+```
+
+<a name="license"></a>
+
+## License
+
+MIT