streamer: put testing_utilities.rs behind dev-context-only-utils #12590

Job	Run time
cargo-test-sbf (token/program)	8m 33s
cargo-test-sbf (instruction-padding/program, token/program-2022, token/program-2022-test)	16m 28s
check	3m 55s
cargo-test-sbf (associated-token-account/program, associated-token-account/program-test)	9m 26s
cargo-test-sbf (token-upgrade/program)	8m 57s
cargo-test-sbf (feature-proposal/program)	8m 7s
test (token/cli, token/program, token/program-2022, associated-token-account/program, instruction...	18m 12s
cargo-test-sbf (governance/addin-mock/program, governance/program)	11m 28s
test (single-pool/cli, single-pool/program)	18m 30s
cargo-test-sbf (memo/program)	7m 7s
test (token-upgrade/cli, token-upgrade/program)	16m 50s
cargo-test-sbf (name-service/program)	10m 48s
cargo-test-sbf (stake-pool/program)	13m 39s
cargo-test-sbf (single-pool/program)	11m 7s
	2h 43m 7s

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