fix(uv): migrate runtime calls to vim.uv

[khaneliman]

Summary

Migrate Neorg's runtime libuv calls from vim.loop to vim.uv.

Why

Neovim deprecates vim.loop, and Neorg requires Neovim 0.10 or newer.

What changed

• Replaced 16 runtime calls across six modules.
• Left doc generation and commented profiling examples unchanged.

Testing

• Changed-file StyLua and Luacheck checks passed.
• All changed Lua files passed a headless parse check.
• A focused libuv namespace check passed.
• The Lux test environment did not finish dependency synchronization locally.

Related Issue(s)

• None.