Run Cypher queries from the rdx console

[paracycle]

Goal

Let rdx console run Cypher directly, addressing the "query mode" idea from #868's review.

What it does

The session is a stock IRB workspace with graph in scope, so plain Ruby works as always (graph["Foo"]). On top of that it registers three things through IRB's own extension APIs:

# `run(<CYPHER>)` — a helper method, so the result is a value you can assign and navigate.
rubydex(main):001> rows = run("MATCH (c:Class)-[:HAS_PARENT]->(p) RETURN c, p")
rubydex(main):002> rows.first["c"].name

# `query <CYPHER>` — a command taking the rest of the line verbatim; prints a formatted table.
rubydex(main):003> query MATCH (n:Class|Module) RETURN n.name ORDER BY n.name

# `schema` — prints the queryable schema.
rubydex(main):004> schema

query takes the rest of the line verbatim, so the Cypher needs neither quoting nor to be valid Ruby. Rather than swapping the REPL's evaluator for a modal toggle, Cypher lines are simply prefixed with query — the clean, idiomatic IRB realization of a query mode. run is the programmatic entry point and query the interactive quick-look; they are deliberately separate rather than one delegating to the other.

How it hooks into IRB

IRB has two distinct registration APIs, and this PR uses each for what it's for:

• IRB::Command.register — for query/schema, which consume the rest of the line verbatim.
• IRB::HelperMethod.register — for run, which must stay an ordinary expression so its value can be assigned.

The session workspace is IRB's own IRB::WorkSpace.new, not a hand-rolled binding. That matters for three reasons:

• self is main and the cref is Object, so class Foo; end at the prompt defines ::Foo. A binding captured inside class << self would define #<Class:Rubydex::Console>::Foo instead.
• No caller locals leak into the prompt. Deriving the binding from the CLI's TOPLEVEL_BINDING would inherit every top-level local of exe/rdx — including query and schema, and a local shadows the IRB command of the same name.
• _, help and the rest of IRB's conveniences behave exactly as in stock irb.

Only graph is injected, via IRB::WorkSpace#local_variable_set.

Notes

• Console logic lives in lib/rubydex/console.rb. Console.run (objects), Console.render (formatted string) and Console.describe_schema are plain module methods, so they are testable without driving IRB.
• Both IRB APIs used here landed in IRB 1.13, so the file activates gem "irb", ">= 1.13" at load. A missing or older IRB raises LoadError (Gem::MissingSpecVersionError is one), which exe/rdx turns into Interactive mode requires \irb` >= 1.13 to be in the bundle` rather than a backtrace. IRB is not declared in the gemspec, which carries no runtime dependencies.
• run returns the rich objects from Query#run (Return Cypher query results as graph objects #873): node columns come back as live Declaration/Definition/Document handles.

Verification

• test/console_test.rb — 8 runs, 29 assertions, 0 failures. Includes a regression test that the session workspace evaluates at top level (self == main, only graph injected, class Probe; end defines ::Probe); it fails if a hand-rolled binding is reintroduced.
• rubocop clean.
• Live smoke test of rdx console against this repo: self → main, local_variables → [:_, :__, :graph], Foo.name → "Foo", run("MATCH (c:Class {name: 'Rubydex::Graph'}) RETURN c.name") → [{"c.name" => "Rubydex::Graph"}], and query/schema both print their tables.
• Degradation checked both ways: with no irb installed, and with only irb 1.12 installed, rdx console aborts cleanly with exit status 1.

[Morriar]

Found one CI issue to fix before this lands.

[Morriar]

You may need to require "fiddle" to fix the Windows build?