Add --test flag to query test-scope classpath (#84)

[rochala]

Problem

Closes #84.

Project-aware commands (get / list / search) only ever resolved the compile-scope classpath, so symbols from test-only dependencies (e.g. munit.FunSuite) were never found. There was no way to reach the test classpath. As the issue notes, sbt's own --module server/Test syntax doesn't work either — cellar just spliced it into server/Test/Compile/fullClasspath, which sbt rejects.

Solution

A --test flag on the project-aware commands selects the test scope. Each build tool maps it to its own model:

Build tool	How test scope is modeled	--test behavior
sbt	config axis (Test)	exports <module>/Test/fullClasspath
scala-cli	config axis (--test)	compiles with --test
Mill	separate sub-module (e.g. foo.test)	rejected with guidance — test code is already reachable via --module foo.test; Mill has no Compile/Test scope axis

The classpath cache key now includes the scope, so compile- and test-scope results don't collide.

Verification

End-to-end, against a real project per build tool, querying a test-only munit dependency:

• sbt multi-module project: search --module core FunSuite → empty; search --module core --test FunSuite → munit.FunSuite ✅
• scala-cli project (//> using test.dep): same before/after --test ✅
• Mill (this repo): search --module lib --test FlatMap → --test is not supported for Mill projects: ... Query it directly, e.g. --module foo.test. (exit 1) ✅

Full lib.test suite passes (372 tests), including a new test for the Mill rejection.

🤖 Generated with Claude Code