feat(php-shim): give ported exceptions PHP's class hierarchy

Ported exceptions were flat structs reached with `downcast_ref`, so
Composer's `catch (\RuntimeException $e)` only matched the exact leaf
type and `get_class($e)` had nothing to report. Each exception now
embeds an instance of the class it extends and travels inside an
`AnyThrowable`; `Catch::catch`/`catch_mut` walk that chain, and
`PhpClass::php_class_name` yields the PHP FQCN.

Dropping the `std::error::Error` impls from the exception types leaves
`AnyThrowable` as the only route into an `anyhow::Error`, so the walk
cannot be bypassed. A `no_exception_downcast` linter catches the
`downcast::<X>()` calls that would now silently answer `None`.

Three sites change behavior as a result: the `TransportException`
exit-code override reaches `MaxFileSizeExceededException`, the
`catch (\LogicException)` in findSimilar() reaches its subclasses, and
rendered exception titles carry the real class name rather than a
guess. `get_class_err()` is no longer a `todo!()`, which re-enables
FilesystemRepositoryTest::testCorruptedRepositoryFile.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

1 files changed, 2 insertions, 1 deletions

diff --git a/crates/shirabe/tests/package/loader/validating_array_loader_test.rs b/crates/shirabe/tests/package/loader/validating_array_loader_test.rs
index 07f3e4a6..1b1ed448 100644
--- a/crates/shirabe/tests/package/loader/validating_array_loader_test.rs
+++ b/crates/shirabe/tests/package/loader/validating_array_loader_test.rs
@@ -4,6 +4,7 @@ use crate::test_case;
 use indexmap::IndexMap;
 use shirabe::package::handle::PackageInterfaceHandle;
 use shirabe::package::loader::{InvalidPackageException, LoaderInterface, ValidatingArrayLoader};
+use shirabe_php_shim::Catch as _;
 use shirabe_php_shim::PhpMixed;
 
 fn s(v: &str) -> PhpMixed {
@@ -792,7 +793,7 @@ fn test_load_failure_throws_exception() {
             Ok(_) => panic!("Expected exception to be thrown"),
             Err(e) => {
                 let exception = e
-                    .downcast_ref::<InvalidPackageException>()
+                    .catch::<InvalidPackageException>()
                     .expect("Expected InvalidPackageException");
                 let mut errors: Vec<String> = exception.get_errors().to_vec();
                 expected_errors.sort();