fix lint: satisfy nilnil in internaldto tests; drop PR_README.md (#235) - #767

This PR fixes lint warnings in the unit test files added in the previous PR (#235)

Changes:

• internal/stackql/internal_data_transfer/internaldto/internaldto_test.go: Added //nolint:nilnil comments to 3 function literals where a nil return value is intentionally passed as a non-error return value, silencing false positive nilnil linter warnings.

Type of change

• Bug fix (non-breaking change to fix a bug).
• Feature (non-breaking change to add functionality).
• Breaking change.
• Other (eg: documentation change). Please explain: lint fix and file cleanup.

Issues referenced

• Unit testing for package primitive_context #235 — Unit testing for package internaldto (internal_data_transfer/internaldto)

Evidence

Local lint run with golangci-lint run — no warnings from the modified file. Full local test suite passing:

$ go test --tags sqlite_stackql ./...
ok github.com/stackql/stackql/internal/stackql/internal_data_transfer/internaldto 0.020s
ok github.com/stackql/stackql/internal/stackql/iqlerror 0.003s
ok github.com/stackql/stackql/internal/stackql/kstore 0.005s
ok github.com/stackql/stackql/internal/stackql/metadatavisitors 0.042s
ok github.com/stackql/stackql/internal/stackql/nativedb 0.003s
ok github.com/stackql/stackql/internal/stackql/providerconfig 0.004s
ok github.com/stackql/stackql/internal/stackql/sqlstream 0.041s
ok github.com/stackql/stackql/pkg/textutil 0.004s
ok github.com/stackql/stackql/pkg/txncounter 0.004s
ok github.com/stackql/stackql/pkg/sqltypeutil 0.009s
... (all other packages pass)

Checklist:

• A full round of testing has been completed, and there are no test failures as a result of these changes.
• The changes are covered with functional and/or integration robot testing.
• The changes work on all supported platforms.
• Unit tests pass locally, as per the developer guide.
• Robot tests pass locally, as per the developer guide.
• Linter passes locally, as per the developer guide.