Add ecalls for hash functions, and SDK helpers; add a test app for the SDK #116

Job	Run time
Build vnd-test on Risc-V target	27s
Run V-App Client SDK tests	50s
Run V-App SDK tests	26s
Run common crate tests	26s
Run vnd-test app tests	28s
Run vnd-test app client tests	59s
Build application using the reusable workflow / Retrieve application metadata / Retrieve application metadata	6s
Build application using the reusable workflow / Build application for NanoS, X, S+, and Stax (nanosp)	3m 17s
Build application using the reusable workflow / Build application for NanoS, X, S+, and Stax (stax)	3m 24s
Build application using the reusable workflow / Build application for NanoS, X, S+, and Stax (flex)	3m 27s
Build application using the reusable workflow / Merge build artifacts	2s
Integration tests on Speculos (nanosplus)	2m 12s
Integration tests on Speculos (flex)	3m 2s
Integration tests on Speculos (stax)	2m 39s
	21m 45s

Provide feedback