optee_teec: extension: fix macro errors

[ivila]

1. Fix usage of Rust types as return values in FFI functions.
   https://github.com/apache/incubator-teaclave-trustzone-sdk/blob/cf0f662eec9213be32bf972888f422575b03bc7a/optee-teec/src/extension.rs#L23-L33
   Currently, the plugin's methods use Rust's optee_teec::Result as the return value for FFI, which is incorrect since Rust does not guarantee a stable ABI. We need to change them to optee_teec_sys::TEEC_Result(alias of u32) instead.

2. Standardize the function signature to require returning a Result.
   Similar to the original signatures of TEEC functions, we currently require the plugin's methods to return an error.

   • For init: from fn() to fn() -> optee_teec::Result<()>
   • For invoke_command: from fn(&mut optee_teec::PluginParameters) to fn(&mut optee_teec::PluginParameters) -> optee_teec::Result<()>

   And in fact, the current examples of supp_plugin-rs already return a Result, even though this contradicts their function signatures.
   

3. Use inner functions in generated code to prevent unexpected early returns.
   Previous macros simply duplicated the code into the new function.
   https://github.com/apache/incubator-teaclave-trustzone-sdk/blob/cf0f662eec9213be32bf972888f422575b03bc7a/optee-teec/macros/src/lib.rs#L60-L67
   Which is buggy if developers have some return statements inside.
   For example, if developer define a function:

   fn init() {
       if method() {
           return;
       }
       // some other codes
   }

   It will be rewrite to:

   #[no_mangle]
   pub fn _plugin_init() -> optee_teec::Result<()> {
       if method() {
           return;  // this line is a syntax error
       }
       // some other codes
       Ok(())
   }

• Fix example: supp_plugin-rs.

[ivila]

Network Error, the pipeline pass on my fork: https://github.com/ivila/incubator-teaclave-trustzone-sdk/actions/runs/14073623792

[ivila]

Update: remove the unnessesary #[no_mangle] tag and re-trigger the pipeline.

[DemesneGH]

Reviewed-by: Yuan Zhuang <yuanz@apache.org>
Thanks!

[DemesneGH]

Please feel free to rebase and merge once CI passed 😄