Add a seekable input stream which spools to a temporary file

[thekid]

This pull request adds io.streams.SpooledInputStream which uses the new seekable buffers from #361

Example

use io\streams\{Buffer, SpooledInputStream};
use lang\Environment;

$socket= /* ... */;

// Buffers to a file in environment's temporary directory by default
$stream= new SpooledInputStream($socket->in());

// Use a Buffer instance for more control. Here, uses 1 MB of memory before writing to a file
$stream= new SpooledInputStream($socket->in(), new Buffer(Environment::tempDir(), 1024 * 1024));

// Skips over 100 bytes, then reads 100 bytes
$stream->seek(100); 
$stream->read(100);

// Seeks back, possible because of backing file buffer, then reads 100 bytes
$stream->seek(0);
$stream->read(100);

$stream->close();

[thekid]

Released in https://github.com/xp-framework/core/releases/tag/v12.10.0