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>

tools/stress.py

@@ -29,17 +29,18 @@ from math import comb
 
 ROOT = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
 sys.path.insert(0, ROOT)
+import tools  # noqa: E402,F401  checks the runtime and puts src/ first on the path, before paperspec is imported
 
-from tools.oracle import align as AL  # noqa: E402
-from tools.oracle import anchors as AN  # noqa: E402
-from tools.oracle import corrections as CO  # noqa: E402
-from tools.oracle import crypto, fingerprint as FP, hashing, jcs, receipts as RC, rights as RI, targets as TG  # noqa: E402
-from tools.oracle import keys as K, log as LG, mldsa, vrf  # noqa: E402
-from tools.oracle import package as PK  # noqa: E402
-from tools.oracle.model import LABELLED, LEAVES, Doc  # noqa: E402
-from tools.oracle.notation import fold_math  # noqa: E402
-from tools.oracle.text import NODE_ID_RE, RECORD_ID_RE, letter_first, norm, record_id, sha256_hex, is_ws  # noqa: E402
-from tools.oracle.tree import Refusal, validate_structure  # noqa: E402
+from paperspec import align as AL  # noqa: E402
+from paperspec import anchors as AN  # noqa: E402
+from paperspec import corrections as CO  # noqa: E402
+from paperspec import crypto, fingerprint as FP, hashing, jcs, receipts as RC, rights as RI, targets as TG  # noqa: E402
+from paperspec import keys as K, log as LG, mldsa, vrf  # noqa: E402
+from paperspec import package as PK  # noqa: E402
+from paperspec.model import LABELLED, LEAVES, Doc  # noqa: E402
+from paperspec.notation import fold_math  # noqa: E402
+from paperspec.text import NODE_ID_RE, RECORD_ID_RE, letter_first, norm, record_id, sha256_hex, is_ws  # noqa: E402
+from paperspec.tree import Refusal, validate_structure  # noqa: E402
 from tools.build import ROSTER_BY_ID, SCHEMAS, secret, sentence_doc, tiny_package  # noqa: E402
 from tools.check import HALE, STORE, TINY_KEY, reference_values  # noqa: E402