Split utils option helpers

[vmoens]

Summary

• move TensorDict repr/lazy/non-tensor/list-stack option state into tensordict._utils_options
• keep tensordict.utils re-exporting the old option helpers and shared _REPR_OPTIONS object
• preserve helper __module__ values as tensordict.utils
• add tests for import identity and shared option state

BC notes

• imports from tensordict.utils and top-level tensordict remain valid
• _REPR_OPTIONS remains the same shared mutable dict object through the facade
• context-manager state is centralized in the new internal module

Test plan

• python -m pytest test/test_utils_options_split.py -q
• python -m pytest test/test_tensordict.py -k "TestSetPrintOptions or set_lazy_legacy or capture_non_tensor_stack" -q
• python -m compileall -q tensordict/utils.py tensordict/_utils_options.py
• import smoke test for _REPR_OPTIONS, get_printoptions, and set_lazy_legacy module/state behavior

[github-actions]

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Current title: Split utils option helpers

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[BugFix] or [Fix]	bug	[BugFix] Fix memory leak in TensorDict
[Feature]	Feature	[Feature] Add new storage backend
[Doc] or [Docs]	documentation	[Doc] Update installation guide
[Refactor]	Refactor	[Refactor] Clean up module imports
[CI]	CI	[CI] Fix workflow permissions
[Test] or [Tests]	Test	[Test] Add unit tests for nn module
[Compile]	Compile	[Compile] Fix torch.compile issue
[Performance] or [Perf]	Performance	[Perf] Optimize tensor operations
[Deprecation]	Deprecation	[Deprecation] Mark old function
[Setup]	setup	[Setup] Update build configuration
[Distributed] or [Dist]	Distributed	[Distributed] Add scatter collective
[Benchmark] or [Bench]	Benchmarks	[Benchmark] Add compile benchmark
[Typing] or [Type]	Typing	[Typing] Add type stubs
[BC-breaking] or [BC]	BC-breaking	[BC-breaking] Remove deprecated API
[Formatting] or [Format]	Formatting	[Format] Fix code style
[Quality]	Quality	[Quality] Improve error messages

Note: Matching is case-insensitive. Common variations (singular/plural) are supported.

[github-actions]

PR Title Label Error

PR title must start with a label prefix in brackets (e.g., [BugFix]).

Current title: Split utils option helpers

Supported Prefixes

Your PR title must start with exactly one of these prefixes (case-insensitive):

Prefix	Label Applied	Example
[BugFix] or [Fix]	bug	[BugFix] Fix memory leak in TensorDict
[Feature]	Feature	[Feature] Add new storage backend
[Doc] or [Docs]	documentation	[Doc] Update installation guide
[Refactor]	Refactor	[Refactor] Clean up module imports
[CI]	CI	[CI] Fix workflow permissions
[Test] or [Tests]	Test	[Test] Add unit tests for nn module
[Compile]	Compile	[Compile] Fix torch.compile issue
[Performance] or [Perf]	Performance	[Perf] Optimize tensor operations
[Deprecation]	Deprecation	[Deprecation] Mark old function
[Setup]	setup	[Setup] Update build configuration
[Distributed] or [Dist]	Distributed	[Distributed] Add scatter collective
[Benchmark] or [Bench]	Benchmarks	[Benchmark] Add compile benchmark
[Typing] or [Type]	Typing	[Typing] Add type stubs
[BC-breaking] or [BC]	BC-breaking	[BC-breaking] Remove deprecated API
[Formatting] or [Format]	Formatting	[Format] Fix code style
[Quality]	Quality	[Quality] Improve error messages

Note: Matching is case-insensitive. Common variations (singular/plural) are supported.