Cost-model package on NPM does not include required files for local compile

[fordN]

Most users will not need to build the native Rust binaries locally on their machine since there are prebuilt binaries hosted on GitHub. However, for some users (primarily those on M1 or M2 macs) there are no prebuilt binaries and the build falls back to compiling the Rust binary locally. In this case, the NPM package does not include all the necessary files for compilation.

error: failed to get `cost-model` as a dependency of package `cost-model-node-plugin v0.1.0 (/indexer/node_modules/@graphprotocol/cost-model)`

Caused by:
  failed to load source for dependency `cost-model`

Caused by:
  Unable to update /indexer/node_modules/@graphprotocol/lang

Caused by:
  failed to read `/indexer/node_modules/@graphprotocol/lang/Cargo.toml`

Caused by:
  No such file or directory (os error 2)

[fordN]

Resolved in #829