[BUG] Multiple select and checkbox arrays are not properly initialized

[lnoor]

Important Notice
We do not provide support through GitHub issues. For community-based help, please use either:

• GitHub Discussions tab
• Our Discord channel

If you're reporting a bug, please continue with this template.

Describe the bug
A clear and concise description of what the bug is.

With a form containing a multiple select box or a set of checkboxes all having the same name the function fill_form()
will not initialize the form properly.
None of the select options and all of the checkboxes are marked as selected or checked.

Minimal Reproducible Example
Provide a minimal code snippet that reproduces the issue. This is crucial for us to understand and fix the bug quickly.

#!/bin/env python3
from fasthtml.common import *

@dataclass
class MultiSelect:
    items: list[str]

select_data = MultiSelect(items=['a', 'c'])
select_form = Form(Select(Option('a', value='a'), Option('b', value='b'), Option('c', value='c'), multiple='1', name='items'))
select_form = fill_form(select_form, select_data)
print(to_xml(select_form))

@dataclass
class MultiCheck:
    items: list[str]

check_data = MultiCheck(items=['a', 'c'])
check_form = Form(Fieldset(Label(Input(type='checkbox', name='items', value='a'), 'a'),
                           Label(Input(type='checkbox', name='items', value='b'), 'b'),
                           Label(Input(type='checkbox', name='items', value='c'), 'c')))
multiform = fill_form(check_form, check_data)
print(to_xml(check_form))

Expected behavior
A clear and concise description of what you expected to happen.

The actual outcome is:

<form enctype="multipart/form-data">
  <select multiple="1" name="items">
    <option value="a">a</option>
    <option value="b">b</option>
    <option value="c">c</option>
  </select>
</form>

and

<form enctype="multipart/form-data">
  <fieldset>
    <label><input type="checkbox" name="items" value="a" checked="1">a</label>
    <label><input type="checkbox" name="items" value="b" checked="1">b</label>
    <label><input type="checkbox" name="items" value="c" checked="1">c</label>
  </fieldset>
</form>

The desired outcome should be:

<form enctype="multipart/form-data">
  <select multiple="1" name="items">
    <option value="a" selected="1">a</option>
    <option value="b">b</option>
    <option value="c" selected="1">c</option>
  </select>
</form>

and

<form enctype="multipart/form-data">
  <fieldset>
    <label><input type="checkbox" name="items" value="a" checked="1">a</label>
    <label><input type="checkbox" name="items" value="b">b</label>
    <label><input type="checkbox" name="items" value="c" checked="1">c</label>
  </fieldset>
</form>

Environment Information
Please provide the following version information:

• fastlite version: 0.0.13
• fastcore version: 1.7.19
• fasthtml version: fasthtml.git@3b6c7000df01bf10329214f4ff13918317f1fd20

Confirmation
Please confirm the following:

• [x ] I have read the FAQ (https://docs.fastht.ml/explains/faq.html)
• [x ] I have provided a minimal reproducible example
• [x ] I have included the versions of fastlite, fastcore, and fasthtml
• [x ] I understand that this is a volunteer open source project with no commercial support.

Additional context
Add any other context about the problem here.

The problem actually resides in the function _fill_item().
I have a fix ready for which I will create a PR.

Screenshots
If applicable, add screenshots to help explain your problem.