[ivila]

Two related optee-teec fixes:

1. Correct ConnectionMethods login-code mapping.
   ConnectionMethods previously derived its discriminants implicitly, but
   TEEC_LOGIN_APPLICATION, TEEC_LOGIN_USER_APPLICATION and
   TEEC_LOGIN_GROUP_APPLICATION are 0x4, 0x5, 0x6 (there is no 0x3),
   so login as u32 could pass a non-existent login code to
   TEEC_OpenSession. The variants are now pinned to the TEEC_LOGIN_*
   constants with #[repr(u32)] and num_enum, with an Unknown(u32)
   catch-all and a round-trip unit test covering every constant.

2. Remove hand-written Send/Sync from Context and Session.

   • Context now holds Arc<Mutex<InnerContext>>, which is automatically
     Send + Sync because raw::TEEC_Context contains only scalars.
   • Session stores the opaque handle in a private
     RawTeecSession(raw::TEEC_Session) wrapper. A single, documented
     unsafe impl Send lives on that wrapper; Session itself is derived.
   • The raw handle is kept opaque and optee-teec-sys is untouched.