Add structured output to `tach report`

[pavelzw]

It would be nice if tach report also supported json output.

Something like this

$ tach report --help
...
  --output        Output format, one of `pretty`, `raw`, `json`

tach report --json my_module
{
  "dependencies": [
    {
      "file_path": "my_module/abc.py",
      "line_number": 44,
      "import": "other_module.abc"
    },
    // ...
  ],
  "usages": ...,
  "external-dependencies": ...
}

[bollwyvl]

Indeed: and a (versioned, published) schema to go with any structured output. A bespoke schema could be derived with e.g. schemars.

Worth considering, though, is Someone Else's Schema, such as SARIF, already conveniently wrapped with serde_sarif. This would provide a direct import path to widely used tools without {m x tach_version} adapters.