Add --refresh option for xts alias with source tracking

[Copilot]

xts alias caches files from URLs and local paths but provided no mechanism to update them when sources change. Additionally, --list showed cached paths instead of original sources, making it unclear where configs originated.

Changes

New JSON structure for aliases.json:

{
  "alias_name": {
    "cached_path": "/home/user/.xts/cache/file.xts",
    "source": "https://example.com/file.xts"
  }
}

• --refresh command: Re-downloads from URLs or re-copies from local files

  xts --alias --refresh myalias

• Source tracking: All aliases now store original source (URL or resolved file path) alongside cached path

• Updated listing: --list displays source location instead of cache path

  $ xts --alias --list
  myalias -> https://example.com/config.xts

• Automatic migration: Old format ({"name": "/path"}) migrates to new format on first load. Migrated aliases show helpful error when refresh is attempted since original source is unknown.

• Helper functions: _get_cached_path() and _get_source() abstract format differences throughout codebase

All existing functionality preserved. Alias resolution still returns cached path for execution.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Task: Refresh option for xts alias</issue_title>
<issue_description>### Goal

When xts alias is used with urls, the files downloaded from these urls are cached. Therefore, a method needs to be in place for users to manually refresh their cached files. For this, a --refresh option could be used with xts alias. e.g. xts alias --refresh <alias name> to cause the cached file to be updated with the latest from the url.</issue_description>

Comments on the Issue (you are @copilot in this section)

@TB-1993 As part of this we should also fix the caching/listing system. For refresh to work the xts_aliases.json will need to contain the original path/url of the .xts file. That's how it will know where to get the new version of the file from. Similarly, when `xts --alias --list` is used it should print out the .xts files original location, not the cached files location.

• Fixes Task: Refresh option for xts alias #50

---

💬 We'd love your input! Share your thoughts on Copilot coding agent in our 2 minute survey.