update waf datetime parsing for different servers #5293

User Story

In order to accurately derive file modified dates from waf source, datagov wants to update waf datetime parsing to handle different formats/servers

Acceptance Criteria

[ACs should be clearly demoable/verifiable whenever possible. Try specifying them using BDD.]

• GIVEN a waf source
  AND a datetime format not like "2025-01-22 23:21" (e.g. "05-Jun-2025 17:17")
  WHEN waf datetime parsing happens
  THEN the other format is parsed correctly \

Background

• we consider the modified date in waf sources to avoid unnecessary downloads (if the source document is older than what we have then skip it)
• currently, our waf datime parsing function only handles "2025-01-22 23:21" format but we want to make sure other formats are supported to. that function will pad with a placeholder datetime but if we can correctly parse the date on the page that would be better.

Security Considerations (required)

[Any security concerns that might be implicated in the change. "None" is OK, just be explicit here!]

Sketch

• identify different datetime formats (based on server? what if the server type isn't in the response header?)
• implement those datetime formats based on the server type? or just try them all