Extract shared query parameter building for issue list operations

Compare the query parameter building in GetRepositoryIssues.apply() and Repository.get_issues(), including their recover blocks, conditionals, and push calls. Read nearby model convenience methods to assess whether a shared helper fits the broader pattern. Done means the duplicated logic is consolidated without changing issue-list query behavior.

The query parameter building logic in GetRepositoryIssues.apply() and Repository.get_issues() is identical — same recover block, same conditionals, same push calls. If a new parameter is added, both sites must be updated in lockstep.

Repository.get_issues() can't delegate to GetRepositoryIssues.apply() because it has a template URL from the API response rather than owner/repo strings. It could potentially delegate differently, or the shared query param building could be extracted into a helper.

This is a pre-existing pattern in the codebase (other convenience methods on models also duplicate param building), so this may be worth addressing more broadly rather than just for issues.