[PTO][IR] tile_subview documented but unknown op; implementation provides subset

[WenboCodes]

Problem

Docs describe pto.tile_subview, but implementation defines pto.subset.

Evidence

• Docs section and example:
  • docs/PTO_IR_manual.md:388
  • docs/PTO_IR_manual.md:420
• Implemented op:
  • include/PTO/IR/PTOOps.td:158 (PTO_SubsetOp with mnemonic subset)

Repro

Using docs example op name leads to:
custom op 'pto.tile_subview' is unknown

Expected behavior

Decide canonical op name and align all surfaces.

• Option A: rename/alias parser to support tile_subview
• Option B: update docs to pto.subset only

Acceptance criteria

• One canonical name (plus optional alias policy).
• Parser/docs/tests aligned.
• Add parser regression test for chosen behavior.