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/text.py

@@ -1,105 +0,0 @@
-"""Text normalization, IDs, keys and small shared helpers.
-
-Non-normative; see spec/01-conventions.md and spec/04-identity.md.
-"""
-
-import hashlib
-import re
-import unicodedata
-
-from . import jcs
-
-# Unicode White_Space=yes (PropList.txt), the set every rule in the spec means by "whitespace".
-WHITE_SPACE = frozenset(
-    [0x09, 0x0A, 0x0B, 0x0C, 0x0D, 0x20, 0x85, 0xA0, 0x1680]
-    + list(range(0x2000, 0x200B))
-    + [0x2028, 0x2029, 0x202F, 0x205F, 0x3000]
-)
-
-
-def is_ws(ch):
-    return ord(ch) in WHITE_SPACE
-
-
-def collapse_ws(s):
-    out = []
-    prev_ws = False
-    for ch in s:
-        if is_ws(ch):
-            if not prev_ws:
-                out.append(" ")
-            prev_ws = True
-        else:
-            out.append(ch)
-            prev_ws = False
-    return "".join(out)
-
-
-def trim(s):
-    a, b = 0, len(s)
-    while a < b and is_ws(s[a]):
-        a += 1
-    while b > a and is_ws(s[b - 1]):
-        b -= 1
-    return s[a:b]
-
-
-def remove_ws(s):
-    return "".join(ch for ch in s if not is_ws(ch))
-
-
-def norm(s):
-    """The hashing normalization: NFC, whitespace runs to one U+0020, trimmed."""
-    return trim(collapse_ws(unicodedata.normalize("NFC", s)))
-
-
-def sha256_hex(b):
-    if isinstance(b, str):
-        b = b.encode("utf-8")
-    return hashlib.sha256(b).hexdigest()
-
-
-def is_digit(ch):
-    return unicodedata.category(ch) == "Nd"
-
-
-def digits(s):
-    return "".join(ch for ch in s if is_digit(ch))
-
-
-# Crockford base32, lowercase.
-ALPHABET = "0123456789abcdefghjkmnpqrstvwxyz"
-LETTERS = "abcdefghjkmnpqrstvwxyz"
-assert len(ALPHABET) == 32 and len(LETTERS) == 22
-
-NODE_ID_RE = re.compile(r"^[a-hjkmnp-tv-z][0-9a-hjkmnp-tv-z]{6}$")
-RECORD_ID_RE = re.compile(r"^[a-hjkmnp-tv-z][0-9a-hjkmnp-tv-z]{6,25}$")
-KEY_RE = re.compile(r"^[a-z0-9][a-z0-9._-]*$")
-HASH_RE = re.compile(r"^[0-9a-f]{64}$")
-
-
-def letter_first(digest, length):
-    """Encode a digest as a letter-first Crockford base32 ID of `length` characters."""
-    first = LETTERS[digest[0] % 22]
-    bits = int.from_bytes(digest[1:], "big")
-    nbits = 8 * (len(digest) - 1)
-    out = [first]
-    for i in range(length - 1):
-        shift = nbits - 5 * (i + 1)
-        out.append(ALPHABET[(bits >> shift) & 31])
-    return "".join(out)
-
-
-def mint_node_id(doc_key, kind, text_hash, occurrence):
-    d = hashlib.sha256(jcs.dumpb(["scienting-id/1", doc_key, kind, text_hash, occurrence])).digest()
-    return letter_first(d, 7)
-
-
-def record_id(record_hash_hex):
-    """A record's ID: 13 letter-first base32 characters of its record hash."""
-    return letter_first(bytes.fromhex(record_hash_hex), 13)
-
-
-def cp_to_utf16(s, offset):
-    """Convert a code point offset in `s` to a UTF-16 code unit offset."""
-    return sum(2 if ord(ch) > 0xFFFF else 1 for ch in s[:offset])