fix(nvim-cmp): preserve sources added by specs in opts function

[vuxuanhungg]

Summary

Fix sources added by specs (e.g. luasnip, lazydev) being silently dropped in the nvim-cmp configuration.

Problem

The opts function builds its own sources table (buffer, nvim_lsp, path) and assigns it directly:

sources = sources,

This overwrites opts.sources, which contains sources added by specs via opts_extend = { "sources" } — such as luasnip (from the LuaSnip spec) and lazydev (from the lazydev spec).
As a result, snippet completions and other spec-injected sources are silently lost.

Fix

Replace the direct assignment with vim.list_extend to merge the locally-built sources with those from specs:

sources = vim.list_extend(sources, opts.sources),

This ensures sources like { name = "luasnip", priority = 750 } and { name = "lazydev", group_index = 0 } are preserved alongside the base sources.

[github-actions]

Review Checklist

Does this PR follow the [Contribution Guidelines](development guidelines)? Following is a partial checklist:

Proper conventional commit scoping:

• If you are adding a new plugin, the scope would be the name of the category it is being added into. ex. feat(utility): added noice.nvim plugin

• If you are modifying a pre-existing plugin or pack, the scope would be the name of the plugin folder. ex. fix(noice-nvim): fix LSP handler error

• Pull request title has the appropriate conventional commit type and scope where the scope is the name of the pre-existing directory in the project as described above

• README is properly formatted and uses fenced in links with <url> unless they are inside a [title](url)

• Entry returns a single plugin spec with the new plugin as the only top level spec (not applicable for recipes or packs).

• Proper usage of opts table rather than setting things up with the config function.

• Proper usage of specs table for all specs that are not dependencies of a given plugin (not applicable for recipes or packs).