load Zig's LLDB pretty printers when debugging with CodeLLDB

[lejmr]

Before: debugging Zig in Zed shows slices and std containers as raw ptr / len / capacity fields.

After:

parts = std.ArrayList(Ast.Node) len=3 capacity=4
  items = []Ast.Node len=3
    [0] = {children:len=0, value:"b", kind:value}

Zig already ships LLDB formatters for this (tools/lldb_pretty_printers.py, MIT). This PR bundles the script, materializes it into the extension's work directory when a CodeLLDB scenario is created, and loads it via initCommands.

Two details worth a reviewer's eye:

• The commands are routed through script + HandleCommand, because a directly failing initCommand aborts the whole CodeLLDB launch — this way a missing/broken script only logs to the debug console and the session runs as before.
• On top of the upstream script there is a small marked section (# Zed zig extension additions) that puts the type into the summary (std.ArrayList(T) len=…) — Zed's Variables panel doesn't render the DAP type field — and registers the string summary for []const u8 (upstream only covers []u8).

Works with any scenario the locator creates (zig test from the gutter, zig build run); combined with #44 it makes test debugging actually pleasant.

Example: