Update tensorstore::Result with some tricks from absl::StatusOr

The main changes are:
* The internal absl::Status is now in a union to do explicit initialization, which omits some double initialization paths, and the default constructor of the internal storage type is deleted.

* More functions have lifetime annotations. absl::StatusOr has some lifetime-based template annotations which are not included here.

* Some slight restructuring of construction and assignment.

PiperOrigin-RevId: 808685870
Change-Id: I7b3709fe0201cbb3c538c04506a3c69745dbb127

Author: laramiel

docs/conf.py

@@ -362,6 +362,11 @@ def _python_type_to_xref(
         'object_type': 'class',
         'desc': 'C++ class',
     },
+    'absl::Status::ok': {
+        'url': 'https://abseil.io/docs/cpp/guides/status#checking-errors',
+        'object_type': 'function',
+        'desc': 'C++ class',
+    },
     'absl::StatusOr': {
         'url': (
             'https://abseil.io/docs/cpp/guides/status#returning-a-status-or-a-value'
@@ -426,6 +431,11 @@ def _python_type_to_xref(
         'object_type': 'class',
         'desc': 'C++ class',
     },
+    'std::move': {
+        'url': 'https://en.cppreference.com/w/cpp/utility/move.html',
+        'object_type': 'function',
+        'desc': 'C++ function',
+    },
 }
 
 for code in [

tensorstore/kvstore/ocdbt/format/data_file_id_codec.cc

@@ -14,16 +14,26 @@
 
 #include "tensorstore/kvstore/ocdbt/format/data_file_id_codec.h"
 
+#include <stddef.h>
+#include <stdint.h>
+
 #include <algorithm>
+#include <cassert>
+#include <cstring>
 #include <string_view>
+#include <utility>
 #include <vector>
 
 #include "absl/container/flat_hash_map.h"
+#include "absl/log/absl_check.h"
+#include "absl/status/status.h"
+#include "absl/strings/str_format.h"
 #include "riegeli/bytes/reader.h"
 #include "riegeli/bytes/writer.h"
 #include "riegeli/varint/varint_reading.h"
 #include "riegeli/varint/varint_writing.h"
 #include "tensorstore/internal/ref_counted_string.h"
+#include "tensorstore/kvstore/ocdbt/format/codec_util.h"
 #include "tensorstore/kvstore/ocdbt/format/data_file_id.h"
 
 namespace tensorstore {

tensorstore/util/BUILD

@@ -523,6 +523,7 @@ tensorstore_cc_test(
 
 tensorstore_cc_library(
     name = "result",
+    srcs = ["result_impl.cc"],
     hdrs = [
         "result.h",
         "result_impl.h",
@@ -534,8 +535,7 @@ tensorstore_cc_library(
         "//tensorstore/internal/preprocessor:cat",
         "//tensorstore/internal/preprocessor:expand",
         "@abseil-cpp//absl/base:core_headers",
-        "@abseil-cpp//absl/log:absl_check",
-        "@abseil-cpp//absl/log:absl_log",
+        "@abseil-cpp//absl/base:nullability",
         "@abseil-cpp//absl/meta:type_traits",
         "@abseil-cpp//absl/status",
     ],