Tracking issue for making CI run faster

[miraclx]

Opening this for visibility.

Current integration tests generate isolated projects with distinct target folders despite compiling ~99% of the same artifacts.

Causing current CI runs to run upwards of an hour.

The following patches reduce the total runtime.

1. #39, based on #35 which removed the intermediate generation, shares a single target directory for all the integration tests.

• Results: CI runs in under 7 minutes. https://github.com/near/cargo-near/actions/runs/2939756365

2. #40, which merges right into main, keeping the intermediate generation, also shares a single target directory for all the integration tests.

• Results: CI runs in under 40 minutes. https://github.com/near/cargo-near/actions/runs/2944084292

3. #42, mix of # 1 and # 2.

• Results: same as # 1.