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/oracle/targets.py

@@ -1,69 +0,0 @@
-"""The target set of targeted F3: the nodes a team's claims, data and quotations rest on.
-
-Non-normative; see spec/08-fidelity.md §8.10.
-"""
-
-from .model import LEAVES, MATH_KINDS
-from .text import is_digit
-
-DIGIT_RULES = ("all", "anchored-sections", "none")
-# The kinds that count as the section a node sits in: a section, or the front or back matter outside any.
-SECTION_KINDS = frozenset(["section", "front", "back"])
-DIGIT_KINDS = frozenset(["sentence", "cell"])
-DIGIT_RUNS = frozenset(["text", "math"])
-
-
-def has_digit_run(node):
-    """Whether a `text` or `math` run of the node holds a digit (General Category Nd)."""
-    for r in node.get("content") or []:
-        if not isinstance(r, dict) or r.get("kind") not in DIGIT_RUNS:
-            continue
-        s = r.get("text") if r["kind"] == "text" else r.get("source")
-        if any(is_digit(ch) for ch in s or ""):
-            return True
-    return False
-
-
-def enclosing_section(doc, nid):
-    """The nearest ancestor-or-self that is a section, or the front or back matter, else the root."""
-    if doc.nodes[nid]["kind"] in SECTION_KINDS:
-        return nid
-    for a in reversed(doc.ancestors(nid)):
-        if doc.nodes[a]["kind"] in SECTION_KINDS:
-            return a
-    return doc.root
-
-
-def target_set(doc, anchored, digit_rule="all"):
-    """The target set as `[[node, reason], …]` in document order, with `reason` the first that applies of
-    `anchored`, `equation` and `digits`.
-
-    `anchored` lists the live nodes that extracts, dataset values, confirmed claim links, draft quotations or
-    pinned citations anchor; a container among them contributes its leaves. Every equation and equation line
-    is a target. Under `all`, so is every sentence or cell with a digit in a text or math run; under
-    `anchored-sections`, only those in a section that holds an anchored node; under `none`, none.
-    """
-    if digit_rule not in DIGIT_RULES:
-        raise ValueError("digit rule must be one of %s" % ", ".join(DIGIT_RULES))
-    anchored = set(anchored)
-    unknown = sorted(a for a in anchored if a not in doc.nodes)
-    if unknown:
-        raise ValueError("anchored nodes are not live: %s" % ", ".join(unknown))
-    reasons = {}
-    for nid in sorted(anchored):
-        if doc.nodes[nid]["kind"] in LEAVES:
-            reasons[nid] = "anchored"
-        else:
-            for leaf in doc.leaves(nid):
-                reasons.setdefault(leaf, "anchored")
-    for nid in doc.preorder():
-        if doc.nodes[nid]["kind"] in MATH_KINDS:
-            reasons.setdefault(nid, "equation")
-    if digit_rule != "none":
-        sections = {enclosing_section(doc, a) for a in anchored}
-        for nid in doc.preorder():
-            n = doc.nodes[nid]
-            if n["kind"] in DIGIT_KINDS and has_digit_run(n):
-                if digit_rule == "all" or enclosing_section(doc, nid) in sections:
-                    reasons.setdefault(nid, "digits")
-    return [[nid, reasons[nid]] for nid in doc.preorder() if nid in reasons]