[CK_BUILDER] conv bwd weight testing

[Snektron]

Proposed changes

NOTE: Targetting #3604, merge that one first and update the target branch (GitHub should implement proper stacked pull requests already).

This adds ckt::run integration for backwards weight algorithms, for the reference kernel, ck, and ck tile.

Design

• Since the Args<> structure is reusable between fwd/bwd wt/bwd data conv, I've split conv_fwd.hpp out into args.hpp and fwd.hpp. The former just contains Args<>, the latter contains Inputs, Outputs, and direction-specific functionality.
• I've moved the headers around a bit to group everything in the testing/conv/ directory, I figured that'd make more sense than having conv/ in all names.
• Since CK requires separate ckt::run implementations for fwd/bwd wt/bwd data, which are relatively large, I put them in separate files fwd_ck.hpp and bwd_weight_ck.hpp.
• The reference and CK tile implementations are identical and easy to abstract, so both fwd and bwd weight are both in reference.hpp and ck_tile.hpp
• The return type of ckt::run was changed to a tuple in [CK_BUILDER] Add grouped conv fwd ck tile profiler #3518. We discussed that throwing exceptions in ckt::run is not desirable, but I don't really like the tuple either. I've written a custom RunResult struct instead, and testing integration so that we can easily check if a run was correctly, for example by doing EXPECT_THAT(ckt::run(...), SuccessfulRun()). If theres a problem then a message is printed.

[Copilot]

Pull request overview

This PR adds backwards weight testing integration for convolution operations, extending the existing ckt::run infrastructure to support backwards weight algorithms alongside the existing forward convolution support.

Changes:

• Introduced RunResult structure to replace tuple return types from ckt::run, providing clearer success/failure semantics
• Reorganized convolution testing headers into a testing/conv/ directory structure
• Added backwards weight support for CK, CK Tile, and reference implementations

Reviewed changes

Copilot reviewed 26 out of 27 changed files in this pull request and generated 12 comments.

Show a summary per file

File	Description
experimental/builder/include/ck_tile/builder/testing/testing.hpp	Adds RunResult struct and updates run() signature to return it
experimental/builder/include/ck_tile/builder/testing/conv/args.hpp	Extracts reusable Args<> structure, removing direction-specific code
experimental/builder/include/ck_tile/builder/testing/conv/fwd.hpp	Defines forward-specific Inputs, Outputs, and initialization
experimental/builder/include/ck_tile/builder/testing/conv/bwd_weight.hpp	Defines backwards weight-specific Inputs, Outputs, and initialization
experimental/builder/include/ck_tile/builder/testing/conv/reference.hpp	Implements reference kernel support for both forward and backwards weight
experimental/builder/include/ck_tile/builder/testing/conv/ck_tile.hpp	Implements CK Tile support for both forward and backwards weight
experimental/builder/include/ck_tile/builder/testing/conv/fwd_ck.hpp	Implements old CK forward convolution support
experimental/builder/include/ck_tile/builder/testing/conv/bwd_weight_ck.hpp	Implements old CK backwards weight convolution support
experimental/builder/test/testing_utils.hpp	Adds SuccessfulRun() matcher and enhances validation error reporting
experimental/builder/test/testing_utils.cpp	Implements RunResultMatcher for testing ckt::run results
Various test files	Updates to use new header locations and SuccessfulRun() matcher

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