fix: remove redundant union of property types in index signature for unknown additionalProperties

When a schema has both `properties` and `additionalProperties: {}` (or `true`),
the generator now emits `[key: string]: unknown` instead of the redundant union
`[key: string]: unknown | string | null | ... | undefined`.

- When additionalProperties is `unknown`, only use it for the index signature type
  (since `unknown` already subsumes all types including `undefined`)
- For typed additionalProperties (e.g. `{ type: 'string' }`), keep current behavior
  of including named property types to satisfy TypeScript's index constraint
- Update all affected test snapshots

Co-authored-by: mrlubos <12529395+mrlubos@users.noreply.github.com>

Author: Copilot

packages/openapi-ts-tests/main/test/__snapshots__/2.0.x/additional-properties-true/types.gen.ts

@@ -6,7 +6,7 @@ export type ClientOptions = {
 
 export type Foo = {
     foo: string;
-    [key: string]: unknown | string;
+    [key: string]: unknown;
 };
 
 export type Bar = Foo & {
@@ -15,7 +15,7 @@ export type Bar = Foo & {
 
 export type Baz = Foo & {
     bar: string;
-    [key: string]: unknown | string;
+    [key: string]: unknown;
 };
 
 export type Qux = {

packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/additional-properties-true/types.gen.ts

@@ -6,7 +6,7 @@ export type ClientOptions = {
 
 export type Foo = {
     foo: string;
-    [key: string]: unknown | string;
+    [key: string]: unknown;
 };
 
 export type Bar = Foo & {
@@ -15,7 +15,7 @@ export type Bar = Foo & {
 
 export type Baz = Foo & {
     bar: string;
-    [key: string]: unknown | string;
+    [key: string]: unknown;
 };
 
 export type Qux = {

packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@angular/common/default-class/types.gen.ts

@@ -703,7 +703,7 @@ export type ModelWithAdditionalPropertiesEqTrue = {
      * This is a simple string property
      */
     prop?: string;
-    [key: string]: unknown | string | undefined;
+    [key: string]: unknown;
 };
 
 export type NestedAnyOfArraysNullable = {

packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@angular/common/default/types.gen.ts

@@ -703,7 +703,7 @@ export type ModelWithAdditionalPropertiesEqTrue = {
      * This is a simple string property
      */
     prop?: string;
-    [key: string]: unknown | string | undefined;
+    [key: string]: unknown;
 };
 
 export type NestedAnyOfArraysNullable = {

packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@hey-api/sdk/default/types.gen.ts

@@ -703,7 +703,7 @@ export type ModelWithAdditionalPropertiesEqTrue = {
      * This is a simple string property
      */
     prop?: string;
-    [key: string]: unknown | string | undefined;
+    [key: string]: unknown;
 };
 
 export type NestedAnyOfArraysNullable = {

packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@hey-api/sdk/throwOnError/types.gen.ts

@@ -703,7 +703,7 @@ export type ModelWithAdditionalPropertiesEqTrue = {
      * This is a simple string property
      */
     prop?: string;
-    [key: string]: unknown | string | undefined;
+    [key: string]: unknown;
 };
 
 export type NestedAnyOfArraysNullable = {

packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@pinia/colada/fetch/types.gen.ts

@@ -703,7 +703,7 @@ export type ModelWithAdditionalPropertiesEqTrue = {
      * This is a simple string property
      */
     prop?: string;
-    [key: string]: unknown | string | undefined;
+    [key: string]: unknown;
 };
 
 export type NestedAnyOfArraysNullable = {

packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/angular-query-experimental/axios/types.gen.ts

@@ -703,7 +703,7 @@ export type ModelWithAdditionalPropertiesEqTrue = {
      * This is a simple string property
      */
     prop?: string;
-    [key: string]: unknown | string | undefined;
+    [key: string]: unknown;
 };
 
 export type NestedAnyOfArraysNullable = {

packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/angular-query-experimental/fetch/types.gen.ts

@@ -703,7 +703,7 @@ export type ModelWithAdditionalPropertiesEqTrue = {
      * This is a simple string property
      */
     prop?: string;
-    [key: string]: unknown | string | undefined;
+    [key: string]: unknown;
 };
 
 export type NestedAnyOfArraysNullable = {

packages/openapi-ts-tests/main/test/__snapshots__/3.0.x/plugins/@tanstack/react-query/axios/types.gen.ts

@@ -703,7 +703,7 @@ export type ModelWithAdditionalPropertiesEqTrue = {
      * This is a simple string property
      */
     prop?: string;
-    [key: string]: unknown | string | undefined;
+    [key: string]: unknown;
 };
 
 export type NestedAnyOfArraysNullable = {