[water] verify index expr step/stride are positive

[ftynse]

Add a verifier that index expression step and stride are strictly
positive to avoid semantically undefined behavior (what does it mean to
have a 0-element piece of the tensor? stride zero is hidden
broadcasting, negative stride is hidden reversal, both are detrimental
to dependence analysis).

Closes #1012.

[Copilot]

Pull request overview

Adds verification to reject semantically undefined Wave index mappings by requiring index-expression step and stride to be strictly positive when they can be folded to a concrete value (with hyperparameters substituted), improving correctness for dependence analysis.

Changes:

• Add Wave dialect verification for strictly-positive step/stride and retain “at most one non-unit step” enforcement when foldable.
• Add MLIR negative tests covering zero/negative step and stride.
• Update ElementsPerThread inference commentary and adjust an inference test setup.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
water/lib/Dialect/Wave/IR/WaveDialect.cpp	Introduces verifier helpers to enforce positive step/stride and integrates them into dialect verification flow.
water/test/Dialect/Wave/ops-invalid.mlir	Adds invalid IR tests asserting new verifier diagnostics for zero/negative step/stride.
water/lib/Dialect/Wave/Transforms/InferTypes.cpp	Updates TODO commentary around redundancy with verifiers and hyperparameter presence.
water/test/Dialect/Wave/propagate-elements-per-thread.mlir	Adjusts a test function’s attributes related to hyperparameters for inference-pass behavior.

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[martin-luecke]

LGTM, just typos

• typo in PR title: strire → stride
• typo in body: deterimental → detrimental