Replace value-based exception catching with reference-based catching to address
GCC warnings about polymorphic type slicing:
```
warning: catching polymorphic type ‘class seastar::rpc::stream_closed’ by value [-Wcatch-value=]
```
When catching polymorphic exceptions by value, the C++ runtime copies the
thrown exception into a new instance of the specified type, slicing the
actual exception and potentially losing important information. This change
ensures all polymorphic exceptions are caught by reference to preserve the
complete exception state.
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
Closesscylladb/scylladb#23064
da9960db1c