feat: add git stash clear command

[tulilirockz]

I just didn't want to run git stash pop for each entry

I'm new to this codebase, though. Could someone sanity check this?

[altsem]

hi @tulilirockz, I suggest we just rip of how Magit works here and make this an addition into src/ops/discard.rs.

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Head:     feat/key-hints feat: show contextual$
Tag:      v0.39.0 (4)

Stashes (2) <--------------------------------------- Select this and press "k"
stash@{0} On feat/split-screen: key-hints
stash@{1} On master: search

Recent commits
9d8653b feat/key-hints feat: show contextual k$
7d72007 origin/master feat: Rename 'Toggle Sec$
ddac3b8 ci: allow workflow_dispatch
2ae7c59 ci: update macos-x64 target from macos$
e8fb628 v0.39.0 chore(release): prepare for v0$
35032dd perf: replace `similar` dep with the m$
d0d5cf0 feat: Gitu now boosts its own - more f$
24f7444 style: add some padding to the menu
aa1b080 fix: discarding files/hunks/lines now $
d15f1e5 refactor: use nom for status parsing








-UUU:%%-  F1  magit: gitu    All   L4     (Magi
Drop all stashes in refs/stash? (y or n)   <----------- This prompt appears

(this is default bound to 'K' in Gitu). You'll find tests in here: src/tests/discard.rs

I've been wanting to improve the prompt in this module, they're all just "Really discard?" - which doesn't tell you a lot about what's going on.