fix(lua): index assignment-style function definitions (#1650) (#1778)

Apply upstream PR #1623 by danusha2345 (fix commit aa777063),
which also addresses #1616, to the current main base. Preserve the
upstream WASM and Rust implementations and regression coverage.

Index assigned locals, table members, static string keys and nested
callback tables as callable symbols, with calls owned by those symbols.
Keep dynamic keys unguessed. Add #1650 to the Unreleased changelog and
retain the existing re-index guidance without an extraction-version bump.

Verified on Linux x64 with Node 22.19.0:
- native kernel build, tsc, asset copy, executable CLI
- issue repro: 3 nodes / 2 edges -> 4 nodes / 4 edges
- EPR.PowerController::SyncHydroPower is indexed; its caller is client.lua
- syncHydroPower depth-2 impact reaches client.lua
- extraction/resolution/Lua parity: 844 tests passed (kernel expected)
- forced-WASM Lua/Luau extraction/resolution: 20 tests passed

Co-authored-by: Colby McHenry <colbymchenry@users.noreply.github.com>

CHANGELOG.md

@@ -213,6 +213,7 @@ and adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 #### Symbols, tests and the viewer
 
+- Lua and Luau function expressions assigned to locals, table members, or keyed table fields are now indexed as callable nodes. Calls from `local f = function() ... end`, `M.f = function() ... end`, and callback tables such as `M.handlers = { onClick = function() ... end }` are attributed to the named function or method instead of collapsing onto the file node, so callers and impact no longer omit these handlers. Re-index after upgrading. (#1616, #1650)
 - **Functions bound with `const` inside another function are symbols now.** `const handleClear = () => {…}` inside a React component — every handler that skips `useCallback` — was invisible to `callers`, `callees` and impact, answering "Symbol not found" exactly the way a function with no callers would. It is indexed like its module-level twin, contained by the enclosing function, with its own calls. Re-index after upgrading. (#1669)
 - `codegraph callers`, `callees`, and `query` now clearly report when their result limit hides additional matches, including exact totals in callers/callees JSON output; the `codegraph_callers` and `codegraph_callees` MCP answers carry the same "showing N of M" note. (#1639, #1674)
 - CommonJS controllers written as `exports.getItems = async (req, res) => {…}` or `module.exports.x = function () {…}` are now indexed as exported functions, so `node`, `callers` and impact find every Express handler in that style and the calls inside them belong to the handler instead of the file. Re-index JavaScript projects after upgrading. (#1675)