refactor: move the reference implementation to src/paperspec

The oracle had two import names, `tools.oracle` for the tools and
`paperspec` for other repositories, which could load the same code twice
in one process and needed a gate keyed on the module name. It now lives
in the standard src layout under its one name.

- git mv tools/oracle -> src/paperspec; the 22 rule modules are unchanged.
- The tools import `paperspec`. `tools/__init__.py` now holds the Python
  3.14 and cryptography/jsonschema check and puts src/ first on sys.path,
  so the tools run this checkout's code with or without pixi. The
  package's own __init__ checks nothing and exposes __version__.
- pyproject.toml: version from git tags via setuptools-scm
  (guess-next-dev, node-and-timestamp, src/paperspec/_version.py,
  gitignored). The packages stay listed rather than found because
  schemas/, sql/ and vectors/ stay at the root: the spec links to them and
  the site serves the schemas at their $id URLs.
- pixi.toml: a `dev` feature and environment with setuptools,
  setuptools-scm and python-build, and `pixi run -e dev wheel`.
- check.py scans src/paperspec for rule IDs; README, CONTRIBUTING, the
  FAQ, the overview, the vectors and tools READMEs and the changelog point
  at the new path. The FAQ no longer says the oracle is not a library.

pixi.lock is not re-solved in this commit: with a dynamic version, pixi
builds the package metadata to lock, which needs the conda environment
installed. Run `pixi lock` and commit the result before pushing; the site
workflow installs with --locked.

pixi run check passes; no computed value, vector, fixture, schema or SQL
file changed.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

pyproject.toml

@@ -1,11 +1,10 @@
 [build-system]
+requires = ["setuptools>=80", "setuptools-scm>=8"]
 build-backend = "setuptools.build_meta"
 
-requires = ["setuptools>=77"]
-
 [project]
 name = "paperspec"
-version = "0.1.0"
+dynamic = ["version"]
 description = "The scienting formats: the reference implementation of every rule, with the JSON Schemas, SQL and test vectors as package data"
 readme = "README.md"
 license = "Apache-2.0"
@@ -32,13 +31,15 @@ Homepage = "https://paperspec.scient.ing"
 Repository = "https://git.scient.ing/infra/paperspec"
 Documentation = "https://paperspec.scient.ing/docs/"
 
-# `tools/oracle` is the package `paperspec`; the schemas, SQL and vectors travel
-# with it as data subpackages, so a consumer reads them with importlib.resources.
+# The code is `src/paperspec`. The schemas, SQL and vectors stay at the repository root, where the
+# specification links to them and the website serves the schemas at their `$id` URLs, and travel with the
+# package as data subpackages, so a consumer reads them with importlib.resources. That mapping is why the
+# packages are listed rather than found.
 [tool.setuptools]
 packages = ["paperspec", "paperspec.schemas", "paperspec.sql", "paperspec.vectors"]
 
 [tool.setuptools.package-dir]
-"paperspec" = "tools/oracle"
+"" = "src"
 "paperspec.schemas" = "schemas"
 "paperspec.sql" = "sql"
 "paperspec.vectors" = "vectors"
@@ -47,3 +48,10 @@ packages = ["paperspec", "paperspec.schemas", "paperspec.sql", "paperspec.vector
 "paperspec.schemas" = ["*.json"]
 "paperspec.sql" = ["*.sql"]
 "paperspec.vectors" = ["*.jsonl"]
+
+# The package version comes from git tags (v0.1.0 builds as 0.1.0, later commits as 0.1.1.devN). It is the
+# version of this code, not of the formats, which CHANGELOG.md and pixi.toml carry.
+[tool.setuptools_scm]
+version_file = "src/paperspec/_version.py"
+version_scheme = "guess-next-dev"
+local_scheme = "node-and-timestamp"