fix(result_builder): match single-test results to discovered IDs

[rcasia]

Summary

Fixes #338.

JUnit Vintage reports a plain method as demo, while discovery identifies it as demo(). Previously, the single-testcase branch returned the report ID directly, leaving Neotest unable to associate a passing result with the discovered test node. A parameterized method with only one invocation had the same problem.

• Share ID matching between single-testcase results and merged parameterized results.
• Prefer an exact discovered ID, then match the class and method name without the parameter signature.
• Preserve single-test failure details and existing fallback behavior for unmatched single results.
• Cover plain Vintage tests, failures on a selected method, single parameterized invocations (Vintage and shortened parameter types), and exact-match precedence.
• Update the result-flow documentation and external tree type annotations.

Verification

• Confirmed the original regression test failed before the fix and passes afterward.
• make test: all 194 cases pass.
• stylua --check .: passes.
• Luacheck and all applicable pre-commit hooks, including the test hook: pass.
• lua-language-server --check .: no problems found.
• All 16 GitHub checks pass, including the unit/integration and E2E matrices on Ubuntu and Windows for Neovim stable, v0.11.7, and nightly.

The PR remains a draft; it now includes the production fix as well as the regression tests.