[FEATURE] Add option to download specific issue or PR by number or ranges

[c-vigo]

Description
Add an action input that lets users sync only selected issues and/or pull requests by specifying one or more numbers or numeric ranges (e.g. a single issue 42, a range 10-20, or a mix like 1,5,10-15).

Problem Statement
Currently the action syncs all issues/PRs (subject to include-closed, updated-since, etc.). There is no way to sync only a subset by issue/PR number. Users who want a single issue, a few specific items, or a range must sync everything and then filter locally, which is slow and wasteful for large repos.

Proposed Solution
Introduce one or more optional inputs, e.g.:

• issues-filter (optional): Comma-separated list of issue numbers and/or ranges (e.g. 1,5,10-20,42). If set, only issues matching these numbers are synced; if unset, behavior is unchanged (sync all issues per existing options).
• prs-filter (optional): Same idea for pull requests.

Parsing rules: allow single numbers and inclusive ranges (min-max). Invalid or empty values can be ignored or surface a clear error. When a filter is provided, it overrides “sync all” for that type (issues or PRs).

Alternatives Considered

• Relying only on updated-since and manual filtering: does not support “only these numbers.”
• Separate actions for “sync one” vs “sync all”: more to maintain; a single action with optional filters is simpler.

Additional Context
Fits with existing inputs (sync-issues, sync-prs, include-closed, updated-since). Implementation will touch the code that decides which issues/PRs to fetch (e.g. REST/GraphQL listing or filtering).

Impact

• Users who need a subset of issues/PRs (e.g. for docs, reports, or local tooling) get faster, smaller syncs.
• Backward compatible: when the new inputs are not set, behavior remains “sync all” as today.
• Changelog: Added — new optional issues-filter / prs-filter (or single combined) input(s) to sync by number or ranges.

TDD

• TDD compliance (see .cursor/rules/tdd.mdc)