fix(lang.omnisharp): update CSharpier command and arguments for Mason compatibility (#6156)

## Description
This PR updates the CSharpier integration in LazyVim to reflect changes
in how Mason installs the formatter.

Previously, Mason installed CSharpier as the `dotnet-csharpier` binary,
which allowed running it without additional arguments. Now, Mason
installs it simply as `csharpier`, requiring the explicit format
argument for it to work correctly.

This change updates the formatter command and arguments accordingly to
ensure compatibility with the latest Mason installation and CSharpier
CLI behavior.

## Changes
Replaced `dotnet-csharpier` with `csharpier` as the executable command.

Added the required `format` argument to the command invocation.

## Related Issue(s)
Fixes #6155

## Checklist
I have read the
[CONTRIBUTING](https://github.com/LazyVim/LazyVim/blob/main/CONTRIBUTING.md)
guidelines.

lua/lazyvim/plugins/extras/lang/omnisharp.lua

@@ -27,12 +27,6 @@ return {
       formatters_by_ft = {
         cs = { "csharpier" },
       },
-      formatters = {
-        csharpier = {
-          command = "dotnet-csharpier",
-          args = { "--write-stdout" },
-        },
-      },
     },
   },
   {