Skip a build directory by its whole name, not by a prefix of it
Independent of #11 and #12.
The discovery walk skipped any directory whose name started with `result`, meaning to skip a nix build output:
```haskell
|| "result" `isPrefixOf` name
```
It also skipped one called `results`, and every package under it went missing from discovery **with nothing reported**. That is what makes it worth a PR rather than a line: a walk that finds no cabal file and a walk that refused to look return the same answer to a caller, so the packages simply were not there.
The fixture fails on master with `Right []` where it wants `Right [PackageName "thing"]`. I checked that before keeping the fix.
## Symlinks are followed
An earlier version of this replaced the name test with a symlink test, on the theory that a nix output is a symlink and what is on the far side of one is not this repository's. That was wrong, and wrong in the same way as the bug: a repository that links a package in on purpose has one to find there, and refusing to follow the link loses it just as silently.
It was also unnecessary. What a `result` actually points at holds no cabal file: in this repository right now it is a check output of `facts.db`, `report.json` and `report.txt`, and a nix source derivation is a tarball. So the walk follows it, lists it, finds nothing, and moves on. `hopinion check .` in this working tree, which has a `result` symlink, reports 0 findings and exits 0 with `result` no longer named anywhere.
And inside a Nix build the source is a store path, so build outputs are not in the tree to begin with.
## What it skips now
`dist-newstyle` and `node_modules` by whole name, because they are real directories holding copies of sources that are not the repository's, and anything hidden for the same reason: `.git`, `.stack-work` and `.direnv` all do.
## Testable
`skippedByName :: Path Rel Dir -> Bool` is top-level and exported, where the walk had it in a `where` clause with no signature and no test. It is pure, so the prefix case is a unit test rather than a walk over a fixture.
187 tests, 9 new: the named and hidden cases, four prefix lookalikes, the fixture with a package two levels under `results`, and one over a temp directory asserting a linked-in package is found.
## One thing worth knowing
The fixture needed a line in `.gitignore`. Your global ignore file has `result*`, which hides a directory called `results` exactly the way this walk did — this repository's own `.gitignore` gets it right with `result` and `result-*`. Same bug one level up, and it silently untracks anything named that way in every repository. I have not touched it.
## Review loop
```
nix flake check
nix develop --command cabal test hopinion-test --test-options="--ai-executor"
```