fix: improve safety when generating field code

[piotr-oles]

This is a part of a bigger project to move away from namespaces.

📦 Published PR as canary version: 0.9.2--canary.40.a1f0e0f.0

✨ Test out this PR locally via:

npm install as-proto-gen@0.9.2--canary.40.a1f0e0f.0
npm install as-proto@0.9.2--canary.40.a1f0e0f.0
# or 
yarn add as-proto-gen@0.9.2--canary.40.a1f0e0f.0
yarn add as-proto@0.9.2--canary.40.a1f0e0f.0

[github-actions]

Benchmark results:

yarn run v1.22.19
$ yarn bench:prepare && yarn bench:run
$ node bench/prepare.js
Generating AssemblyScript protobuf file...
Building AssemblyScript bench file...
$ node bench/index.cjs
benchmarking encoding performance ...

as-proto x 1,144,012 ops/sec ±0.21% (97 runs sampled)
protobuf.js x 561,269 ops/sec ±0.41% (93 runs sampled)
JSON x 448,870 ops/sec ±0.19% (96 runs sampled)
google-protobuf x 293,855 ops/sec ±15.04% (92 runs sampled)

               as-proto was fastest
            protobuf.js was 51.0% ops/sec slower (factor 2.0)
                   JSON was 60.8% ops/sec slower (factor 2.5)
        google-protobuf was 77.6% ops/sec slower (factor 4.5)

benchmarking decoding performance ...

as-proto x 909,567 ops/sec ±0.33% (94 runs sampled)
protobuf.js x 1,354,582 ops/sec ±0.09% (97 runs sampled)
JSON x 434,804 ops/sec ±0.77% (97 runs sampled)
google-protobuf x 289,600 ops/sec ±0.42% (98 runs sampled)

            protobuf.js was fastest
               as-proto was 33.0% ops/sec slower (factor 1.5)
                   JSON was 68.1% ops/sec slower (factor 3.1)
        google-protobuf was 78.7% ops/sec slower (factor 4.7)

benchmarking combined performance ...

as-proto x 511,351 ops/sec ±0.15% (99 runs sampled)
protobuf.js x 383,486 ops/sec ±0.56% (95 runs sampled)
JSON x 194,890 ops/sec ±1.12% (91 runs sampled)
google-protobuf x 149,016 ops/sec ±0.12% (97 runs sampled)

               as-proto was fastest
            protobuf.js was 25.3% ops/sec slower (factor 1.3)
                   JSON was 62.3% ops/sec slower (factor 2.6)
        google-protobuf was 70.9% ops/sec slower (factor 3.4)

Done in 72.47s.

[github-actions]

🚀 PR was released in v0.9.2 🚀