Separate "segment" required field from affecting length field

[theosanderson]

At some point we could rework this to separate it in the query params from the length field so it doesn't interact with the length field but we can make a new issue for this, which I'll do now

Originally posted by @theosanderson in #6057

[claude]

This issue may be related to existing issues: #5840 (Segment presence filter / length checkboxes) and #5993 (SearchUI: show sequence filters not segment-related). Please check if there is overlap with those issues.