Support matrix include and exclude expansions

[gjkim42]

What type of PR is this?

/kind api

What this PR does / why we need it:

Adds GitHub-compatible strategy.matrix.include and strategy.matrix.exclude
transformations. Exclusions remove partial matches before includes are applied;
includes can augment original combinations in declaration order or append
standalone combinations, and include-only matrices are supported.

The workflow parser now preserves axis declaration order, validates bounded
scalar transformation mappings, and applies the 256-job limit to the final
transformed set. Expanded values continue through the existing matrix expression
context and WorkflowJob.spec.matrix.values, preserving stable child identity,
max-parallel scheduling, and result aggregation.

The previous matrix model decoded every matrix key as a scalar axis and only
computed a Cartesian product, so mapping-valued transformations were rejected.

Which issue(s) this PR is related to:

Fixes #65

Special notes for your reviewer:

This keeps matrix values scalar and does not change the WorkflowJob schema or
job-plan version. Strategy fail-fast remains unsupported.

Validation completed with make test and make verify.

Does this PR introduce a user-facing change?

Workflows can use matrix `include` and `exclude` transformations, including include-only matrices.