Fix edit_insert MethodError in debug-mode keymap fallback on Julia 1.12

[mattlie82]

Title: Fix MethodError in debug-mode keymap fallback on Julia 1.12

Body:

Summary

Fixes #420.

On Julia 1.12, loading Debugger and then typing a character that Debugger's )-keymap intercepts (but isn't handling directly, e.g. the cursor isn't at position 0) throws:

MethodError: no method matching edit_insert(::REPL.LineEdit.PromptState, ::REPL.LineEditREPL, ::String)

Root cause

In install_repl_mode, the fallback action for the ) key defaults to the raw LineEdit.edit_insert function when nothing else is already bound to that key:

key_action = get(main_mode.keymap_dict, key, LineEdit.edit_insert)

This is later called with the keymap dispatch's calling convention, key_action(s, args...), which passes (state, repl, char) — 3 arguments. On older Julia versions, edit_insert apparently had a 3-argument method compatible with this convention, so the raw function happened to work. Julia 1.12 only defines 2-argument methods for edit_insert ((state, char)), plus an unrelated MIState catch-all, so the 3-argument call now fails.

Fix

Wrap the fallback in a small closure that matches the keymap's actual (state, repl, char) calling convention, and have it forward only (state, char) to the real edit_insert:

key_action = get(main_mode.keymap_dict, key, (s, repl, c) -> LineEdit.edit_insert(s, c))

If ) is already bound to some other action in main_mode.keymap_dict (e.g. by another package), that binding is used unchanged — this only changes the default fallback.

Testing

• Verified on Julia 1.12.7 and 1.10.7 (aarch64-apple-darwin14): using Debugger no longer errors on load, and typing ) both enters debug> mode at an empty prompt and inserts the character normally elsewhere.
• Ran the existing test suite locally with no new failures.
• (Fill in here if you also tested against 1.10/1.11 via juliaup — worth doing before merge, since the fix changes behavior for all Julia versions, not just 1.12.)