Erlang go-to-definition and hover docs

[JesseHerrick]

#30

• Reuses cached tokenized Elixir documents across LSP handlers to avoid repeated tokenization for completions, aliases/imports/uses, buffer functions, and alias-block checks.
• Adds token-aware completion context detection so completions ignore strings, comments, and heredocs while still handling Erlang atom modules and dotted module/function prefixes.
• Hardens the persistent BEAM formatter process by synchronizing stderr capture, restarting when .formatter.exs changes outside DidSave, and invalidating BEAM processes on formatter watcher events.
• Fixes umbrella formatter config resolution by searching for .formatter.exs up to the LSP project root, so child apps without their own formatter config use the umbrella root config. Closes use umbrella root formatter config when present #35 and Root .formatter.exs support for umbrella projects #34.

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Note

High Risk
High risk due to a large refactor of the persistent formatter into a multiplexed BEAM process plus new Erlang definition/hover/completion paths, touching core LSP request handling, process management, and caching/concurrency.

Overview
Adds a new persistent beam_server.exs that multiplexes formatting and CodeIntel over a framed binary protocol (requests/responses/notifications), including OTP module warmup, Erlang source/doc lookup, exports, and runtime fingerprinting.

Replaces the old single-purpose persistent formatter (formatter_server.exs) with a shared per-_build BEAM process in Go, including request demux by request_id, notification handling, stderr tail capture for crash diagnostics, and restart/eviction on .formatter.exs changes (including umbrella-aware config lookup).

Extends LSP features to support Erlang atom module references (:code.all_loaded) for go-to-definition and hover, adds Erlang module/function completions backed by warmed OTP module/exports caches, and introduces token-aware CompletionContextAtCursor to avoid offering completions inside strings/comments and to better handle : vs ::.

Updates snippet insertion (pipe-aware argument indices) and adds snippet completions for Elixir special forms when the client supports snippets, with expanded test coverage for BEAM protocol behavior, formatter config reloads, and Erlang features.

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