Add suspend() and resume() for MCP clients

[thekid]

This allows to resume an MCP HTTP server session when re-connecting. When resuming, the protocol initialization can be omitted, thus saving multiple roundtrips.

use use io\modelcontextprotocol\McpClient;

$suspens= 'suspense.json';
if (file_exists($suspense)) {
  $client= McpClient::resume(json_decode(file_get_contents($suspense), true));
} else {
  $client= new McpClient($argv[1]);
}

// [...call tools etcetera...]

file_put_contents($suspense, json_encode($client->suspend()));

[thekid]

This needs a check if the transport is resumeable