Simplify ort session management

[javiermtorres]

Currently, there are three places where a session builder (and a session from there) are created:

encoderfile/encoderfile/src/runtime/loader.rs

Line 40 in af055cd

ort::session::Session::builder()?.commit_from_memory(buf.as_slice())?

encoderfile/encoderfile/src/dev_utils/mod.rs

Line 66 in af055cd

ort::session::Session::builder()

encoderfile/encoderfile/src/builder/model.rs

Line 79 in af055cd

Ok(Session::builder()?.commit_from_file(file)?)

It would be good to rearrange these actions in the build and runtime sections:

• Set up tracing before state loading
  • Currently some ort actions are not visible due to late tracing setup (it will also help our own tracing)
• Create a common builder for all necessary sessions
  • We will likely want to use the same options for all sessions we create, and it'll be good to have those options in a single place
• Create/access a session where needed from the existing builder