perf: skip npm install if graph has no new packages

[dsherret]

old is main, deno_new is #23979, target/release/deno is this PR

Benchmark 1: ../../deno/target/release/deno run -A repro.ts
  Time (mean ± σ):     323.7 ms ±   4.3 ms    [User: 245.3 ms, System: 86.2 ms]
  Range (min … max):   319.4 ms … 330.7 ms    10 runs
 
Benchmark 2: ../../deno/deno_new run -A repro.ts
  Time (mean ± σ):     450.2 ms ±   5.4 ms    [User: 365.8 ms, System: 108.6 ms]
  Range (min … max):   443.7 ms … 458.3 ms    10 runs
 
Benchmark 3: ../../deno/deno_old run -A repro.ts
  Time (mean ± σ):     538.5 ms ±   7.2 ms    [User: 445.9 ms, System: 103.2 ms]
  Range (min … max):   531.7 ms … 552.3 ms    10 runs
 
Summary
  ../../deno/target/release/deno run -A repro.ts ran
    1.39 ± 0.02 times faster than ../../deno/deno_new run -A repro.ts
    1.66 ± 0.03 times faster than ../../deno/deno_old run -A repro.ts

Still more to come. We can skip building the entire graph in this case, but right now I'm having it still do it so that we get rid of these other perf issues.

Waiting on #23979

[bartlomieju]

LGTM, impressive improvements