fix(turbo_json): avoid workspace validation errors (#10211)
### Description
#10083 introduced a bug where we swallow validation errors and end up
silently ignoring these workspace `turbo.json` files. This PR fixes that
by distinguishing a missing `turbo.json` from a failed read.
The bug stems from the fact that a missing file and a failed read were
both errors so `turbo_json.or(turbo_jsonc)` could choose a missing
turbo.json error (which is fine, not all workspaces need `turbo.json`s)
over a validation error for the file that is present. We replace `.or`
with an extremely explicit `match` that goes through all the possible
combinations.
### Testing Instructions
Added unit test
Quick manual verification
```
[0 olszewski@macbookpro] /Users/olszewski/code/vercel/turborepo $ turbo_dev build
WARNING No locally installed `turbo` found. Using version: 2.4.5-canary.6.
turbo 2.4.5-canary.6
turbo_json_parse_error
× Failed to parse turbo.json.
╰─▶ × Found an unknown key `lol`.
╭─[cli/turbo.json:9:7]
8 │ "rust-src": {
9 │ "lol": true,
· ─────
10 │ "env": [
╰────
```
