py/scalar: consolidation and code-size reduction

[haydnv]

This PR is a broad Python client simplification and ergonomics pass focused on one goal: make URI/state/ref construction follow a single obvious path and remove legacy/transitional indirection.

What changed

• Moved fully to direct URI(...) construction and removed URI.of(...) usage across runtime/tests.
• Simplified URI handling rules:
  • keep URI typed in domain logic,
  • convert to string only at wire boundaries (JSON keys, HTTP/kernel paths).
• Added URI.with_authority(...) and used it to remove repeated authority-rewrite boilerplate.
• Removed redundant URI patterns like URI(path=URI(...)) and tc.URI(path=tc.URI(...)).
• Made symbolic boxing state-generic:
  • autobox now accepts object/Any and returns State,
  • preserves non-scalar State values,
  • supports numpy-native tensor boxing to Tensor.
• Continued scalar/state hierarchy cleanup:
  • reduced helper duplication,
  • simplified op/ref path composition,
  • removed unnecessary compatibility-style branching.
• Refactored opref/executor path flow:
  • oprefs normalize path via str(...),
  • removed extra path/body indirection in executor.
• Consolidated tensor dtype URI handling and fixed canonical numeric dtype paths expected by local backend.
• Added/updated style guards to prevent regressions:
  • ban URI(...).path constructor extraction,
  • ban redundant str(URI(<already URI>)) wrapping,
  • ban URI.parse(str(...)) churn outside uri.py.
• Updated tests throughout to reflect the new canonical URI + symbolic behavior.

Result

• Cleaner and smaller symbolic/runtime surface.
• More consistent URI ergonomics.
• Fewer transitional helpers and less repetitive code.
• Full test suite passes: 525 passed, 4 skipped.