Add attachment commands (write/ls/read/rm)

[atimin]

Closes #152

Please check if the PR fulfills these requirements

• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)
• CHANGELOG.md has been updated (for bug fixes / features / docs)

What kind of change does this PR introduce?

Feature + Fix

What was changed?

• Added a new top-level attachment command in reduct-cli.
• Implemented attachment subcommands:
  • attachment write <ENTRY_PATH> <KEY> <JSON>
  • attachment ls <ENTRY_PATH>
  • attachment read <ENTRY_PATH> [KEY ...]
  • attachment rm <ENTRY_PATH> <KEY ...> or attachment rm <ENTRY_PATH> --all
• Added shared entry path parsing for ALIAS_OR_URL/BUCKET/ENTRY (including base-path URLs).
• Added consistent handling for entries without attachment metadata (entry/$meta not found -> empty set for read/list operations).
• Added tests for argument validation and end-to-end attachment behavior (write/read/list/remove).
• Fixed cp progress estimation:
  • use time-window-based progress when no limit is set (aligned to entry oldest/latest and --start/--stop),
  • use record-count-based progress when limit is set via --limit or --when ($limit).
• Reduced duplication in attachment/cp tests and helper flows.
• Updated CHANGELOG.md under Unreleased.
• Included existing branch changes removing local .vscode files and refreshing dependency lockfile versions.

Related issues

• Support for Entry Attachments #152

Does this PR introduce a breaking change?

No.

Other information:

• attachment rm now requires an explicit remove target: key(s) or --all.