BFD-4707: Eob updates for previous and next links on patient searches - #3156

JIRA Ticket:
BFD-4707

What Does This PR Do?

• Applies links to ExplanationOfBenefit for patient searches that that have more records that the limit allows
• Adopting _offset as the primary parameter for offsets/startindex
  • We will still respect startIndex if _offset is not provided to avoid a breaking change
  • All offsets in links will use _offset expect for self which will return whatever the server was given.

What Should Reviewers Watch For?

Take note of the comments to how it is determined to add the links

If you're reviewing this PR, please check for these things in particular:
Look at the method used to determine if there is next. A case could be made to make it a little more explicit. I chose not to for performance reasons to avoid processing streams more than needed.

What Security Implications Does This PR Have?

Please indicate if this PR does any of the following:

There are no security concerns with the PR. It only adds additional model detail to request reponses.

• I have considered the above security implications as it relates to this PR. (If one or more of the above apply, it cannot be merged without the ISSO or team security engineer's (@sb-benohe) approval.)
• I have created tests to sufficiently ensure the reliability of my code, if applicable. If this is a modification to an existing piece of code, I have audited the associated tests to ensure everything works as expected.

Validation

The links in the FHIR json are now present

{
  "resourceType": "Bundle",
  "id": "06fa4107-507e-4d3a-9b1e-f4b8ff9822a1",
  "meta": {
    "lastUpdated": "2026-06-04T10:03:39.072-05:00"
  },
  "type": "searchset",
  "total": 2,
  "link": [
    {
      "relation": "next",
      "url": "http://localhost:8080/v3/fhir/ExplanationOfBenefit?patient=284934751&_count=2&startIndex=4"
    },
    {
      "relation": "previous",
      "url": "http://localhost:8080/v3/fhir/ExplanationOfBenefit?patient=284934751&_count=2"
    },
    {
      "relation": "self",
      "url": "http://localhost:8080/v3/fhir/ExplanationOfBenefit?_count=2&patient=284934751&startIndex=2"
    }
  ],
  "entry": []
 }