Bug: generator should not rely on parsed data, in particular dates

The generator methods currently rely on the parsed message to create the hash.
This is subject to change if the parsing should ever change.
For example, headers might be unwrapped (or wrapped), and spacing may change if the parsing library is updated.

A particular problem is that the date is currently converted into UTC by the cluster generator.
The library does not currently do much validation of the format (for example, the following date parses OK: 'Tue, 13 Jul 2004 17:09:03 -429496729500')

However if the validation is ever changed, then the date input to the hash will change. Given that the actual date is irrelevant to the hash, it should be treated the same as any other header, i.e. as textual input only.

If the parsed message is to be used for the hash, then headers need to be normalised before use.

Start by tracing the generator methods, especially the cluster generator, and inspect where the parsed message and date enter hash construction. Compare that path with the original textual headers and date input. Done means hash inputs remain stable when parsing, date conversion, header wrapping, spacing, or validation behavior changes.

Written by the indexing model from the issue text.