codegen: Introduce a new codegen using prost

[justxuewei]

This pull request introduces a new feature, prost, for the ttrpc-rust. The Prost is a modern Protobuf compiler that leverages the power of procedural macro of Rust. Currently, the prost version supports sync, async, and streaming. Here is part of the directory structure:

.
|-- codegen: The new codegen using prost
|-- compiler
|-- example2: Examples for the new codegen
|-- install_protoc.sh: Install protoc on the local environment
|-- src: The ttrpc-rust's src
`-- ttrpc-codegen

The ttrpc-rust is compatible with the older version, while there are certain differences:

1. Protoc is required.
2. Enable "prost" feature for the ttrpc-rust, e.g. ttrpc = { version = "1.0", features = ["prost"] }.
3. Generated Rust files are named based on their proto's package name, rather than the proto filename.
4. Some variable names are different, e.g. for "cpu", CPU is generated by the Rust-protobuf, and Cpu is generated by the Prost.

"example2" gives some examples on how to use it. The functionalities are completely the same as "example".

Fixes: #170

---

codegen: Introduce a new codegen using prost

This pull request refactors the ttrpc-codegen and the compiler, and merges the two crates into a single crate, named "codegen". The codegen uses prost crate, a protobuf compiler for Rust.

Signed-off-by: Xuewei Niu niuxuewei.nxw@antgroup.com

---

ttrpc-rust: Support the new version of codegen

The ttrpc provides a "prost" feature to support the new version of
codegen. An "example2" has been added to demonstrate how to use the
codegen.

Signed-off-by: Xuewei Niu niuxuewei.nxw@antgroup.com

---

ci: Add codegen-related ci testing

Install protoc when executing make deps of the ttrpc. Add codegen's
check and build, and example2' build to the ci testing.

Signed-off-by: Xuewei Niu niuxuewei.nxw@antgroup.com

---

codegen: Fix issues reported by cargo clippy

Fix all issues reported by cargo clippy to make ci testing pass.

Signed-off-by: Xuewei Niu niuxuewei.nxw@antgroup.com

[codecov]

Codecov Report

Base: 25.71% // Head: 25.64% // Decreases project coverage by -0.08% ⚠️

Coverage data is based on head (ce4775e) compared to base (3522dac).
Patch has no changes to coverable lines.

❗ Current head ce4775e differs from pull request most recent head bfa8710. Consider uploading reports for the commit bfa8710 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #173      +/-   ##
==========================================
- Coverage   25.71%   25.64%   -0.08%     
==========================================
  Files          16       16              
  Lines        2399     2406       +7     
==========================================
  Hits          617      617              
- Misses       1782     1789       +7     

Impacted Files	Coverage Δ
src/common.rs	34.57% <0.00%> (-1.00%)	⬇️
src/sync/client.rs	0.00% <0.00%> (ø)
src/asynchronous/client.rs	0.00% <0.00%> (ø)
src/asynchronous/server.rs	0.00% <0.00%> (ø)

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[wllenyj]

Use anyhow="1.0" directly.

[Tim-Zhang]

Hold this and going to reopen it when we need replace rust-protobuf in the future