fix(mcp): restore 4.3 CI after #8522

[soyuka]

#8522 landed on 4.3 in a broken state, in two separate ways. This makes 4.3 green again.

Context: #8522 was based on main, so squash-merging it onto 4.3 wrote main's tree into the maintenance branch (changelog, COMPOSER_ROOT_VERSION: 5.0.x-dev, ^5.0@alpha across 21 components, the Doctrine filter rewrites, the tools/ relocation). That has since been reverted on 4.3. Removing the pollution exposed two real defects that the ^5.0@alpha pin had been masking.

1. Missing BadRequestException (fix(metadata))

src/Mcp references ApiPlatform\Metadata\Exception\BadRequestException, which only existed from 4.4 onwards. With the correct ^4.3 metadata constraint restored:

Error: Class "ApiPlatform\Metadata\Exception\BadRequestException" not found

The file is copied verbatim from 4.4 (byte-identical there and on main), so merging up is a no-op for it. It is self-contained — extends \RuntimeException, implements ExceptionInterface + HttpExceptionInterface, both already on 4.3 with a matching contract.

Fixes the 6 api-platform/mcp jobs (2 errors each) and PHPStan (PHP 8.5) (4 errors, all in Mcp/Tests/Server/HandlerTest.php).

2. Stale tools/list schema expectation (fix(mcp))

#8522 rewrote array type nodes into anyOf branches in Mcp\JsonSchema\SchemaFactory (for #8504 — several MCP clients reject an array type), but never updated the functional test asserting the old shape:

-'status' => ['type' => ['string', 'null']],
+'status' => ['anyOf' => [['type' => 'string'], ['type' => 'null']]],

This one assertion is the sole failure in all 11 PHPUnit jobs on 4.3 (1 failure out of ~2008 tests in each).

Expected effect

Job	Before	After
PHPUnit (...) × 11	1 failure each, all McpTest::testToolsList	fixed
PHPUnit api-platform/mcp × 6	2 errors each	fixed
PHPStan (PHP 8.5)	4 errors	fixed