[REFACTOR] Remove runtime/object.py shim and route Object via tvm_ffi

[tqchen]

Summary

TVM-side cleanup that drops the python/tvm/runtime/object.py shim and
routes tvm.runtime.Object directly to tvm_ffi.Object. The
tvm.runtime.Object re-export is preserved (now a re-export of
tvm_ffi.Object) so external callers keep working.

The load-bearing __object_repr__ install — which wires TVM IR objects
up to the rich C++ ReprPrinter registered through
init_ffi_api("node", ...) — moves into python/tvm/runtime/_ffi_node_api.py.
That module is already imported as a side-effect-only module from
python/tvm/runtime/__init__.py, so the override fires at the right
time (after init_ffi_api registers the C++ printer).

_ffi_node_api.AsRepr itself is kept: tvm_ffi's default repr is
primitive (ClassName(ptr)); TVM IR objects need the rich printer
registered via init_ffi_api("node", ...). AsRepr is what bridges
that printer back into Python repr(obj) and is also the runtime-only
fallback when libtvm.so is unavailable.

The 7 in-tree importers of the deleted shim (plus one straggler in
runtime/disco/session.py) are switched to either
from tvm.runtime import Object or from tvm_ffi import Object,
depending on which pattern the file already uses.

Test plan

• python -c "import tvm; print(repr(tvm.IRModule({})))" produces
  TVMScript-style output (rich repr preserved).
• pytest tests/python/all-platform-minimal-test/ -x — 75 passed,
  77 skipped (matches baseline).
• pytest tests/python/tirx-base/ -x — 273 passed, 2 skipped.
• pre-commit run --files <changed files> — all hooks pass.
• CI green.

[gemini-code-assist]

Code Review

This pull request refactors the TVM runtime by removing the python/tvm/runtime/object.py module and consolidating the Object class imports. The initialization logic for the object representation (object_repr) has been moved to python/tvm/runtime/_ffi_node_api.py, and multiple files have been updated to import Object directly from tvm.runtime or tvm_ffi. I have no feedback to provide.