Added support for converting VectorFst to ConstFst to ffi/python lib … #1219

Job	Run time
Check rust formatting	12s
Check python formatting	5s
Fetch or Build OpenFST (ubuntu-latest)	12s
Fetch or Build OpenFST (macos-13)	13s
rust-clippy	23s
python-doc	52s
rust-doc	15s
rustfst-python (ubuntu-latest)	43s
rustfst-python (macos-13)	1m 21s
rustfst-python-bench	2m 37s
rust-tests (1.74.0, ubuntu-latest, --all --benches --examples --bins --tests)	2m 30s
rust-tests (1.74.0, ubuntu-latest, --manifest-path rustfst/Cargo.toml --features "state-label-u32")	2m 7s
rust-tests (1.74.0, macos-13, --all --benches --examples --bins --tests)	2m 9s
rust-tests (1.74.0, macos-13, --manifest-path rustfst/Cargo.toml --features "state-label-u32")	2m 14s
rust-tests (stable, ubuntu-latest, --all --benches --examples --bins --tests)	1m 52s
rust-tests (stable, ubuntu-latest, --manifest-path rustfst/Cargo.toml --features "state-label-u32")	1m 55s
rust-tests (stable, macos-13, --all --benches --examples --bins --tests)	2m 0s
rust-tests (stable, macos-13, --manifest-path rustfst/Cargo.toml --features "state-label-u32")	2m 8s
Publish rustfst-python's doc	53s
Publish Rust Crate to Crates.io	0s
Publish Python Wheels to PyPI	0s
	24m 41s

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