feat(nix): add Nix language support for nested scope detection

- Add nix.lua with Nix-specific treesitter node types
- Enables chunk indicators for let expressions, attrsets, lambdas, etc.
- Provides better visual feedback for Nix flake structure

This allows hlchunk to show arrows/indicators for all nested scopes
in Nix files (inputs, outputs, let blocks, attribute sets, etc.)
instead of just top-level scopes.

Author: Parker Settle

lua/hlchunk/utils/ts_node_type/init.lua

@@ -3,6 +3,7 @@ local M = {}
 M.cpp = require("hlchunk.utils.ts_node_type.cpp")
 M.css = require("hlchunk.utils.ts_node_type.css")
 M.lua = require("hlchunk.utils.ts_node_type.lua")
+M.nix = require("hlchunk.utils.ts_node_type.nix")
 M.rust = require("hlchunk.utils.ts_node_type.rust")
 M.yaml = require("hlchunk.utils.ts_node_type.yaml")
 M.zig = require("hlchunk.utils.ts_node_type.zig")

lua/hlchunk/utils/ts_node_type/nix.lua

@@ -0,0 +1,17 @@
+-- Nix-specific treesitter node types for hlchunk
+-- Covers: let expressions, attribute sets, lambda functions, with expressions, etc.
+-- Format: node_type = true (table with keys, not array)
+return {
+    let_expression = true,          -- let ... in ...
+    attrset_expression = true,      -- { ... }
+    rec_attrset_expression = true,  -- rec { ... }
+    list_expression = true,         -- [ ... ]
+    lambda_expression = true,       -- arg: body
+    function_expression = true,     -- { args }: body  
+    with_expression = true,         -- with ...; ...
+    if_expression = true,           -- if ... then ... else ...
+    assert_expression = true,       -- assert ...; ...
+    binding = true,                 -- name = value;
+    inherit = true,                 -- inherit ...;
+    inherit_from = true,            -- inherit (...) ...;
+}