Replace wk8/go-ordered-map with pb33f/ordered-map

[samlown]

Summary

• Swaps github.com/wk8/go-ordered-map/v2 for its API-compatible fork github.com/pb33f/ordered-map/v2.
• This removes the indirect dependency on github.com/mailru/easyjson, which has been flagged as a supply-chain risk due to its maintainers' affiliation with VK Group (see Consider removing easyjson dependency due to security risks #182).
• Only the import path changes — the OrderedMap[K, V] type, New[K, V]() constructor, and Set/Get/Delete methods used by this library are unchanged, so NewProperties() and Schema.Properties keep the same shape.
• go mod tidy also bumps the stretchr/testify minimum to v1.11.1 (required by pb33f) and pulls in go.yaml.in/yaml/v4 as a new indirect dep.

Compatibility note

Consumers that reference the fully-qualified type *orderedmap.OrderedMap[string, *Schema] (e.g. when constructing a Schema literal) will need to update their import from github.com/wk8/go-ordered-map/v2 to github.com/pb33f/ordered-map/v2. Users of jsonschema.NewProperties() are unaffected. Worth calling out in release notes.

Fixes #182

Test plan

• go build ./...
• go vet ./...
• go test ./...
• go mod why -m github.com/mailru/easyjson confirms it is no longer a dependency

🤖 Generated with Claude Code

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.34%. Comparing base (0d5bd75) to head (d8cc8eb).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #189   +/-   ##
=======================================
  Coverage   89.34%   89.34%           
=======================================
  Files           4        4           
  Lines         732      732           
=======================================
  Hits          654      654           
  Misses         59       59           
  Partials       19       19           

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