feat: docker build fixes

[ratankaliani]

Issue Overview

Previously, Docker builds were failing for 2 issues.

1. Because setting CARGO_TARGET_DIR in the local environment did not carry into Docker, the build location of the program did not match the expected build directory in copy_elf_to_output_dir.

   Error: No such file or directory (os error 2)

2. The program directory was not canonicalized in create_docker_command, resulting in StripPrefixError if the specified program path in build_program_with_args was a relative path and Docker mode was on.

Ex.

 --- stderr
   thread 'main' panicked at /Users/ratankaliani/.cargo/registry/src/index.crates.io-6f17d22bba15001f/sp1-build-1.1.0/src/docker.rs:42:50:
   called `Result::unwrap()` on an `Err` value: StripPrefixError(())

Resolution

• Set CARGO_TARGET_DIR explicitly with -e in the Docker command.
  • Explicitly write the Docker ELF's to a new subdirectory to ensure that the built ELFs are from Docker compilation.
• Canonicalize the program directory in the Docker command.