fix(util): skip replace_termcodes for plain lhs (fixes Cyrillic 'р' bug #169)

[muratovv]

Summary

Fixes #169 — long-standing bug where Cyrillic mappings containing the letter 'р' (U+0440) require a phantom keypress and render with artifacts like `рþX → +1 keymap` in the popup.

Root cause

`M.norm(lhs)` in `lua/which-key/util.lua` always normalizes through:

```lua
vim.fn.keytrans(vim.api.nvim_replace_termcodes(lhs, true, true, true))
```

The third `true` flag (`special`) makes `replace_termcodes` treat any raw `0x80` byte as a stray `K_SPECIAL` marker and pad it with `X` disambiguation (bytes `FE 58`).

For UTF-8 sequences whose continuation byte is `0x80` — most visibly Cyrillic `р` (`D1 80`) — this corrupts the lhs.

Trace for `"пр"` (bytes `D0 BF D1 80`):

step	result
`Util.t("пр")`	`D0 BF D1 80 FE 58` (`"прX"`)
`keytrans(...)`	`"прþX"` (7 bytes)
`Util.keys(...)`	`{"п", "р", "þ", "X"}` — 4 entries, not 2
`Triggers.add`	registers `vim.keymap.set(mode, "прþX", …)` → vim ambiguity-waits for phantom `X`

Cyrillic `р` is the only single Cyrillic letter affected — every other character in the alphabet has a continuation byte `!= 0x80`. The issue extends to any user mapping whose lhs contains a `р` (e.g. `р`, `gр`, `пр`, etc.).

Fix

Skip `replace_termcodes` when `lhs` has no `<...>` notation. Plain text (latin / unicode / cyrillic) has nothing for `replace_termcodes` to expand, so the round-trip is a no-op except for this K_SPECIAL corruption.

```lua
function M.norm(lhs)
if M.cache.norm[lhs] then return M.cache.norm[lhs] end
if not lhs:find("<", 1, true) then
M.cache.norm[lhs] = lhs
else
M.cache.norm[lhs] = vim.fn.keytrans(M.t(lhs))
end
return M.cache.norm[lhs]
end
```

5 lines of behavioral change. Strings containing `<` (``, ``, ``, ``, etc.) still go through the existing path, preserving termcode handling.

Before / after

Headless probe (`Util.keys` direct call):

input	before	after
`"пр"`	`{"п", "р", "þ", "X"}` ❌	`{"п", "р"}` ✅
`"пд"`	`{"п", "д"}` ✅	`{"п", "д"}` ✅
`"gh"`	`{"g", "h"}` ✅	`{"g", "h"}` ✅
`""`	`{""}` ✅	`{""}` ✅

User-visible: popup popup hints work correctly for Cyrillic prefixes; mappings fire on the first keypress; no `рþX` artifact.

Tests

Added 3 cases to `tests/util_spec.lua` (`"пр"`, `"пд"`, `"шгр"`). All 59 existing tests still pass.

```
$ ./scripts/test
tests/buf_spec.lua: o
tests/layout_spec.lua: oooooooooooooooooooo
tests/mappings_spec.lua: oooooooo
tests/util_spec.lua: oooooooooooooooooooooooooooooo

Fails (0) and Notes (0)
```

Notes

• Tested locally on a real LazyVim config with Cyrillic shortcut layer (`пр`/`пд`/`шг`) — both popup hints and mapping firing work as expected.
• This sidesteps the workaround `desc = "which_key_ignore"` that the community has been recommending for years (it silences the popup at the cost of discoverability).