perf(core): defer clipboard because xsel and pbcopy can be slow (#4120)

## Description

<!-- Describe the big picture of your changes to communicate to the
maintainers
  why we should accept this pull request. -->

See [this](https://github.com/LazyVim/LazyVim/discussions/4112)
discussion

TLDR: 
Startup time performance is affected quite significantly when the
clipboard provider is `xsel`(linux) or `pbcopy`(macos). I expect an
improvement in these cases, especially on older pc's.

This PR resets `vim.opt.clipboard` after the `options` are loaded. Then,
on `VeryLazy`, the setting is restored.

I also tested with `yanky`.

Relevant prints:

1. Before resetting `vim.opt.clipboard` in `init`,
`vim.print(vim.opt.clipboard)` yields a table which will be captured:

```lua
--- fields
_name = "clipboard",
_value = "unnamedplus",
--- more fields
```

2. Set `vim.opt.clipboard = ""` and `vim.print(vim.opt.clipboard)`, also
yields a table:

```lua
--- fields
_name = "clipboard",
_value = "",
--- more fields
```


## Related Issue(s)

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  If this PR fixes any issues, please link to the issue here.
  - Fixes #<issue_number>
-->

## Screenshots

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## Checklist

- [x] I've read the
[CONTRIBUTING](https://github.com/LazyVim/LazyVim/blob/main/CONTRIBUTING.md)
guidelines.

Co-authored-by: abeldekat <abel@nomail.com>

lua/lazyvim/config/init.lua

@@ -161,6 +161,7 @@ end
 
 ---@type LazyVimOptions
 local options
+local lazy_clipboard
 
 ---@param opts? LazyVimOptions
 function M.setup(opts)
@@ -181,6 +182,9 @@ function M.setup(opts)
         M.load("autocmds")
       end
       M.load("keymaps")
+      if lazy_clipboard ~= nil then
+        vim.opt.clipboard = lazy_clipboard
+      end
 
       LazyVim.format.setup()
       LazyVim.news.setup()
@@ -285,6 +289,9 @@ function M.init()
   -- this is needed to make sure options will be correctly applied
   -- after installing missing plugins
   M.load("options")
+  -- defer built-in clipboard handling: "xsel" and "pbcopy" can be slow
+  lazy_clipboard = vim.opt.clipboard
+  vim.opt.clipboard = ""
 
   if vim.g.deprecation_warnings == false then
     vim.deprecate = function() end