chore: miscellaneous RNTuple improvements (#1250)

* Fixed __len__ method

* Added a few more useful methods

* Use the right number in arrays method

* Updated to match spec and did some cleanup

* Fixed order of extra type information

* Extract column summary flags

* style: pre-commit fixes

* Fixed conflict resolution

* Fixed test

* Switched to using enums

* Fixed RNTuple anchor

* Updated locator types

* Removed UserMetadata envelope

* Started implementing new real32 types

* Updated sharded cluster to match spec

* Removed user metadata from footer

* Fixed ClusterSummaryReader

* Fix cascadentuple

* Introduced RNTupleField class

* Added test for #1285

* Fixed test

* Fix test (attempt 2)

* Finalized first version of RNTupleField

* Added tests for RNTupleField

* Implemented iterate method

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

Author: ariostas

src/uproot/const.py

@@ -5,7 +5,7 @@
 """
 from __future__ import annotations
 
-import struct
+from enum import IntEnum
 
 import numpy
 
@@ -118,8 +118,6 @@
 kStreamedMemberWise = numpy.uint16(1 << 14)
 
 ############ RNTuple https://github.com/root-project/root/blob/master/tree/ntuple/v7/doc/specifications.md
-_rntuple_frame_format = struct.Struct("<Q")
-rntuple_env_header = _rntuple_frame_format.pack(0)  # TODO: need to check this
 rntuple_col_num_to_dtype_dict = {
     1: "uint64",
     2: "uint32",
@@ -149,6 +147,8 @@
     26: "int64",  # split + zigzag encoding
     27: "int32",  # split + zigzag encoding
     28: "int16",  # split + zigzag encoding
+    29: "float32trunc",
+    30: "float32quant",
 }
 rntuple_col_num_to_size_dict = {
     1: 64,
@@ -179,6 +179,8 @@
     26: 64,  # split + zigzag encoding
     27: 32,  # split + zigzag encoding
     28: 16,  # split + zigzag encoding
+    29: 32,  # TODO: variable size
+    30: 32,  # TODO: variable size
 }
 
 rntuple_col_type_to_num_dict = {
@@ -212,7 +214,49 @@
     "splitzigzagint16": 28,
 }
 
-rntuple_role_leaf = 0
-rntuple_role_vector = 1
-rntuple_role_struct = 2
-rntuple_role_union = 3
+
+class RNTupleLocatorType(IntEnum):
+    STANDARD = 0x00
+    LARGE = 0x01
+    DAOS = 0x02
+
+
+class RNTupleEnvelopeType(IntEnum):
+    RESERVED = 0x00
+    HEADER = 0x01
+    FOOTER = 0x02
+    PAGELIST = 0x03
+
+
+class RNTupleFieldRole(IntEnum):
+    LEAF = 0x00
+    VECTOR = 0x01
+    STRUCT = 0x02
+    UNION = 0x03
+    UNSPLIT = 0x04
+
+
+class RNTupleFieldFlag(IntEnum):
+    REPETITIVE = 0x01
+    PROJECTED = 0x02
+    CHECKSUM = 0x04
+
+
+class RNTupleColumnFlag(IntEnum):
+    DEFERRED = 0x08
+    RANGE = 0x10
+
+
+class RNTupleExtraTypeIdentifier(IntEnum):
+    ROOT = 0x00
+
+
+class RNTupleUserMetadataType(IntEnum):
+    INT = 0x01
+    BOOL = 0x02
+    DOUBLE = 0x03
+    STRING = 0x04
+
+
+class RNTupleClusterFlag(IntEnum):
+    SHARDED = 0x01