feat: install tools/oracle as the paperspec package

Other repositories (paperstack, then paperpack) import the reference
implementation instead of reimplementing the specification; scienting-core
will take the role later behind the same vectors.

- pyproject.toml: distribution and import name `paperspec`, version 0.1.0,
  Python >= 3.12, no base dependencies; `tools/oracle` is the package, and
  `schemas/`, `sql/` and `vectors/` ship as the data subpackages
  `paperspec.schemas`, `paperspec.sql` and `paperspec.vectors`. Extras
  `schema`, `crypto` and `tools`.
- tools/oracle/__init__.py: the Python 3.14 and cryptography/jsonschema gate
  runs only when imported as `tools.oracle` by the repository's own tools.
- crypto.py imports `cryptography` on first use of HKDF and Ed25519, with an
  ImportError naming `paperspec[crypto]`; schema.py imports `jsonschema` and
  `referencing` in `Store.validator` and `Store.registry`. package.py, db.py
  and receipts.py then import on a bare interpreter.
- pixi.toml installs the package editable (pixi.lock re-solved; no conda pin
  changed), so the tools and the package resolve to the same code.
- tools/README.md names the library surface and the extras; CHANGELOG.md
  records the packaging change under 0.1.0, since check.py requires the
  changelog's first heading to equal the format version.

No computed value, vector, fixture, schema or SQL file changed.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

tools/oracle/schema.py

@@ -3,14 +3,12 @@
 Non-normative.
 The spec's schemas are restricted to the keywords below (spec/22-conformance.md) so that every 2020-12
 validator reads them alike; `lint` refuses any schema that leaves the subset.
+`jsonschema` and `referencing` are imported on first use, so `Store.load`, `deref` and `lint` work without them.
 """
 
 import json
 import os
 
-from jsonschema import Draft202012Validator
-from referencing import Registry, Resource
-
 KEYWORDS = {
     "$schema", "$id", "$ref", "$defs", "$comment", "title", "description", "examples", "default", "deprecated",
     "type", "enum", "const", "properties", "required", "additionalProperties", "patternProperties",
@@ -36,6 +34,8 @@ class Store:
 
     def registry(self):
         if self._registry is None:
+            from referencing import Registry, Resource
+
             names = sorted(f for f in os.listdir(self.root) if f.endswith(".schema.json"))
             self._registry = Registry().with_resources(
                 [(self.load(f)["$id"], Resource.from_contents(self.load(f))) for f in names])
@@ -43,6 +43,8 @@ class Store:
 
     def validator(self, name):
         if name not in self._validators:
+            from jsonschema import Draft202012Validator
+
             self._validators[name] = Draft202012Validator(self.load(name), registry=self.registry())
         return self._validators[name]