feat: move march back-compat auth tests to optional backcompat suite (#127)

Move auth/2025-03-26-oauth-metadata-backcompat and
auth/2025-03-26-oauth-endpoint-fallback out of the required
authScenariosList into a new backcompatScenariosList.

These test backward compatibility with the old 2025-03-26 auth spec
(no PRM, OAuth metadata at server root) which is not part of the
current spec requirements.

- Add new 'backcompat' client suite
- Back-compat scenarios remain in the 'all' suite
- Removed from 'core' and 'auth' suites
- Add separate test describe block for back-compat scenarios

Closes #126

src/index.ts

@@ -18,7 +18,8 @@ import {
   listAuthScenarios,
   listMetadataScenarios,
   listCoreScenarios,
-  listExtensionScenarios
+  listExtensionScenarios,
+  listBackcompatScenarios
 } from './scenarios';
 import { ConformanceCheck } from './types';
 import { ClientOptionsSchema, ServerOptionsSchema } from './schemas';
@@ -69,6 +70,7 @@ program
           all: listScenarios,
           core: listCoreScenarios,
           extensions: listExtensionScenarios,
+          backcompat: listBackcompatScenarios,
           auth: listAuthScenarios,
           metadata: listMetadataScenarios,
           'sep-835': () =>
@@ -182,7 +184,7 @@ program
         console.error('\nAvailable client scenarios:');
         listScenarios().forEach((s) => console.error(`  - ${s}`));
         console.error(
-          '\nAvailable suites: all, core, extensions, auth, metadata, sep-835'
+          '\nAvailable suites: all, core, extensions, backcompat, auth, metadata, sep-835'
         );
         process.exit(1);
       }