Add `calculated_comment_close_date` and `comment_close_date` on the document level

[patphongs]

What we’re after

Update the rulemaking API to support comment close dates at the document level instead of only at the rulemaking level, so that multiple documents within a rulemaking can correctly reflect distinct comment deadlines per document.

It should look similar to this:

"documents": 
[
    {
    "doc_category_id": 4,
    "doc_category_label": "Federal Register Document",
    "doc_date": "2025-03-18",
    "doc_description": "federal register document-hz.pdf",
    "doc_entities": [],
    "doc_id": 365602,
    "doc_type_id": 28,
    "doc_type_label": "NPRM",
    "filename": "federal register document-hz",
    "is_comment_eligible": true,
    NEW "calculated_comment_close_date": "2026-03-31T23:59:59",
    NEW "comment_close_date": "2026-03-31T23:59:59",
    "is_key_document": false,
    "level_1": 2,
    "level_1_label": "NPRM",
    "level_2": 0,
    "level_2_label": "NPRM",
    "level_2_labels": [],
    "sort_order": 0,
    "url": "[/files/legal/rulemakings/2025-99/365602/federal-register-document-hz.pdf](https://api-stage.open.fec.gov/files/legal/rulemakings/2025-99/365602/federal-register-document-hz.pdf)"
    }
]

Completion criteria

• API is updated to include document-level comment_close_date and calculated_comment_close_date date fields.