Position of the INFOs in votables

### Description

In VOTables, the INFOs that are in VOTABLE or RESOURCE can be either on top or at the bottom. See section 7.1 of the standard:


Maybe it's a bug, maybe I didn't find how, but I couldn't add an INFO at the bottom of a RESOURCE.

So I tried to read this file:

```xml

```

Called `test.vot` with:

```python
from astropy.io.votable import parse
table = parse("test.vot")
table.to_xml("output.vot")
```

The output file is now:

```xml

```

We can see that astropy took an info below a table, and wrote it before the table.

### Expected behavior

I would expect:
- to be able to add an info either before or after the data when instantiating a `VOTableFile` object within astropy
- the order to be respected when the table goes through I/O

### Possible solution

The only other VOTable parser I know has two types of INFO structures, a normal one called `info`, and an other one called `post_info`. See its documentation https://github.com/cds-astro/cds-votable-rust/tree/main/crates/cli

Maybe something similar could be implemented here? Otherwise maybe the `Info` class could have a `post` attribute (a boolean) to tag whether this is coming before or after the data?

### How to Reproduce

### Versions

```python
import astropy
try:
astropy.system_info()
except AttributeError:
import platform; print(platform.platform())
import sys; print("Python", sys.version)
import astropy; print("astropy", astropy.__version__)
import numpy; print("Numpy", numpy.__version__)
import erfa; print("pyerfa", erfa.__version__)
try:
import scipy
print("Scipy", scipy.__version__)
except ImportError:
print("Scipy not installed")
try:
import matplotlib
print("Matplotlib", matplotlib.__version__)
except ImportError:
print("Matplotlib not installed")
```
```
platform
--------
platform.platform() = 'Linux-6.1.131-1-MANJARO-x86_64-with-glibc2.41'
platform.version() = '#1 SMP PREEMPT_DYNAMIC Thu Mar 13 15:02:58 UTC 2025'
platform.python_version() = '3.13.0'

packages
--------
astropy 7.0.0
numpy 2.2.2
scipy --
matplotlib --
pandas --
pyerfa 2.0.1.5
```

Start with the astropy.io.votable.parse and VOTableFile entry points, the Info class, and to_xml using the supplied XML example. Trace how an INFO after a TABLE is represented and serialized. Done means INFO placement can be selected when constructing a VOTableFile and a parse/to_xml round trip preserves whether it appears before or after the table.

Written by the indexing model from the issue text.