Adds two improvements to the user/org/repo project-board REST API:
* state filter on column-issues endpoints (issue #4)
GET /api/v1/{users,orgs}/{name}/-/projects/{id}/columns/{col}/issues
GET /api/v1/repos/{owner}/{repo}/projects/{id}/columns/{col}/issues
Now accept ?state=open|closed|all (default open), matching the convention
on the project-list endpoint and on /repos/.../issues. Applied at the
IssuesOptions layer so all three scopes inherit the filter.
* populated num_issues / num_open_issues / num_closed_issues on column-list
(issue #5)
ColumnList.LoadIssueCounts runs two grouped queries against project_issue
joined with issue (one open, one closed). All three List*Columns handlers
call it before converting, so num_issues stops being null and consumers
can render a kanban summary in a single round trip instead of N+1.
Tests:
* unit: empty-input fast path on ColumnList.LoadIssueCounts.
* integration: extended testAPIListProjectColumnIssues / -User / -Org to
close an issue, then verify default=open hides it, state=closed and
state=all return it, and the column-list response carries the correct
open/closed/total split.
Closes#4, closes#5
Oleks