fix: support Lua 5.5 prefix local attributes

[Ne9roni]

Summary

Fix parser support for Lua 5.5 prefix local attributes in local declarations.

This fixes valid Lua 5.5 code such as:

local <close>x = ...
local <const>x = 1

which was previously reported as invalid syntax.

Changes

• allow prefix local attributes in local declarations for Lua 5.5
• keep prefix local attributes gated by runtime version
• reject invalid local <attr> function ... forms
• update parser tests for Lua 5.5 prefix <close> / <const>

Notes

While validating this change against the Lua 5.5 compiler, I found that the previous test expectation around multiple <close> variables in a single local declaration was incorrect.

Lua 5.5 allows prefix local attributes, but it does not allow multiple to-be-closed variables in the same local declaration list. This PR updates the parser behavior and tests to match the actual Lua 5.5 compiler behavior.

[gemini-code-assist]

Code Review

This pull request introduces support for Lua 5.5 prefix local attributes, such as local <close>x. The changes involve updating the parser to handle both prefix and suffix attributes, merging them during variable creation, and implementing validation for the <close> attribute across Lua 5.4 and 5.5. A review comment suggested refactoring the logic for identifying variables without attributes into a helper function to enhance code readability.

[gemini-code-assist]

This block of code to find the first variable without attributes could be extracted into a helper function to improve the readability and maintainability of checkLocalCloseList.

For example, you could create a helper function like this:

local function findFirstVarWithoutAttrs(n2, nrest)
    if n2 and not n2.attrs then
        return n2
    end
    if nrest then
        for i = 1, #nrest do
            if not nrest[i].attrs then
                return nrest[i]
            end
        end
    end
    return nil
end

Then, this block could be simplified to a single line:
local extra = findFirstVarWithoutAttrs(n2, nrest)