Add support for 'orjson' and introduce a 'ResponseDecoder' API for deserialization

[sirosen]

Based on #1384 . This is an alternative to #1383.

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In order to support orjson for serialization, add a new OrjsonRequestEncoder, which mirrors the JSONRequestEncoder type.

The transport can select which encoder to use based on an init-time flag.
This setting highlights the awkwardness of the class-level (read: global) mapping of strings to encoders. Therefore, it is now copied into an instance attribute, which is then post-hoc modified if use_orjson=True.

On the decoding side, the story is more complex, as the objects doing decoding are various: responses, errors, and retry hooks. Only one of those three (retry hooks) operates at the abstraction layer of the transport. Therefore, the changes to support a defined decoder type, and provide it in these contexts, are as follows:

• RetryContext objects now include the response decoder

• response objects use their client object's decoder (specifically, self.client.transport.decoder)

• API errors have their own decoder setting, which can be injected via a contextvar API, but which is not publicly controllable via init -- this avoids compatibility issues around changing the init signature of our error types

Selection of orjson is provided via an init arg to the transport and via an env var, GLOBUS_SDK_USE_ORJSON=1. If the setting is enabled but orjson is not installed, instantiating encoders and decoders (of the Orjson* types) will emit errors, to provide an early-error experience.

Because API errors now need access to globus_sdk.transport, these import paths are more heavily implicated in other parts of the SDK.
This breaks tests which help enforce deferred imports of requests, due to its very slow import time. To rectify, a number of requests imports, specifically, are now TYPE_CHECKING flagged and deferred.

Tests are extended to cover orjson testing, including several new tests, an orjson dependency group, new frozen requirements, tox config, and CI config. Because responses read the client's decoder, a large number of test tweaks are needed to provide a "better" client mock which satisfies this requirement.

In CI and the default tox env list, we only test orjson on a small selection of Python versions, to moderate the expansion of our test matrix.

Diff Info

GitHub's diff looks massive because it's counting all those lines of lockfile/frozen-deps content. True diff is much more modest, but still nontrivial:

$ git diff main --shortstat -- src tests
 29 files changed, 530 insertions(+), 112 deletions(-)

Changelog

Added

• The SDK now supports use of orjson as an alternative JSON encoder and decoder.
  When GLOBUS_SDK_USE_ORJSON=1 is set, request sending and response decoding will use orjson.

  • Use of orjson is optional, but if the variable is set and orjson is not installed, errors will be emitted.

  • The setting can also be configured on transport objects with the init option, use_orjson=True.

  • In a future major version of the SDK, use of orjson will default to true when it is available.