fix: adapt to Neovim 0.12 match node lists

[crisidev]

Problem

On Neovim 0.12, opening any nix file throws for every buffer and breaks highlighting:

.../hmts.nvim/plugin/hmts.lua:127: attempt to call method 'parent' (a nil value)

Cause

Neovim 0.12 removed the all = false mode for query predicates/directives. The match table passed to handlers now always maps a capture to a list of nodes (TSNode[]) instead of a single TSNode. hmts_path_handler and hmts_inject_handler still index it as a single node, so match[predicate[2]]:parent() runs against a plain list table and parent is nil.

Fix

Add resolve_node helper that unwraps the list to its node (with a nil guard) and use it at both handler call sites. Backwards compatible, on older Neovim the value is still a single node and is returned unchanged.

Tested on Neovim 0.12.2.

[gemini-code-assist]

Code Review

This pull request introduces a resolve_node helper function in plugin/hmts.lua to handle changes in Neovim 0.12, where captured matches are returned as a list of nodes instead of a single node. The review feedback suggests a more robust way to distinguish a list of nodes from a single TSNode by using Neovim's built-in list detection APIs (vim.islist or vim.tbl_islist) instead of checking for the absence of a parent field.

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