Make it possible to query by attributes via key-value pairs

### Description

Before:

```
$blocks = \Alley\WP\match_blocks(
$post,
[
'attrs' => [
[
'key' => 'align',
'value' => 'right',
],
],
'name' => 'core/paragraph',
]
);
```

After:

```
$blocks = \Alley\WP\match_blocks(
$post,
[
'attrs' => [
'align' => 'right',
],
'name' => 'core/paragraph',
],
);
```

### Use Case

The reason that this syntax isn't supported is so that the `attrs` parameter behaves like `meta_query`, `tax_query`, etc. I still like that consistency, but I also still get annoyed at having to write the whole thing out, so maybe the consistency isn't worth it.