Refactor codegen/src/generator.rs into a modular directory structure and fix compilation errors.

Co-authored-by: openhands <openhands@all-hands.dev>

Cargo.lock

@@ -310,12 +310,6 @@ dependencies = [
  "itertools",
 ]
 
-[[package]]
-name = "critical-section"
-version = "1.2.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "790eea4361631c5e7d22598ecd5723ff611904e3344ce8720784c93e3d83d40b"
-
 [[package]]
 name = "crossbeam-deque"
 version = "0.8.6"
@@ -353,16 +347,6 @@ version = "1.15.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "48c757948c5ede0e46177b7add2e67155f70e33c07fea8284df6576da70b3719"
 
-[[package]]
-name = "embedded-alloc"
-version = "0.5.1"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "ddae17915accbac2cfbc64ea0ae6e3b330e6ea124ba108dada63646fd3c6f815"
-dependencies = [
- "critical-section",
- "linked_list_allocator",
-]
-
 [[package]]
 name = "env_filter"
 version = "1.0.1"
@@ -793,12 +777,6 @@ version = "0.2.186"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "68ab91017fe16c622486840e4c83c9a37afeff978bd239b5293d61ece587de66"
 
-[[package]]
-name = "linked_list_allocator"
-version = "0.10.6"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "2b23ac50abb8261cb38c6e2a7192d3302e0836dac1628f6a93b82b4fad185897"
-
 [[package]]
 name = "linux-raw-sys"
 version = "0.12.1"
@@ -860,7 +838,7 @@ name = "no_std_test"
 version = "0.1.0"
 dependencies = [
  "bytes",
- "embedded-alloc",
+ "prost",
  "roto-runtime",
 ]