This PR suppresses the following backtrace of `Interrupt` (Ctrl+c) exception for stdio server:
## Before
```console
$ ./examples/stdio_server.rb
^C/Users/koic/src/github.com/modelcontextprotocol/ruby-sdk/lib/mcp/server/transports/stdio_transport.rb:20:
in 'IO#gets': Interrupt
from /Users/koic/src/github.com/modelcontextprotocol/ruby-sdk/lib/mcp/server/transports/stdio_transport.rb:20:
in 'MCP::Server::Transports::StdioTransport#open'
from ./examples/stdio_server.rb:95:in '<main>'
$ echo $?
130
```
## After
```console
$ ./examples/stdio_server.rb
^C
Exiting...
$ echo $?
130
```
This change should prevent unexpected backtrace from appearing when running the example:
https://github.com/modelcontextprotocol/ruby-sdk?tab=readme-ov-file#stdio-transport
85252e0546