Refactor diagnose functions for scaling out other package managers

[kyoshidajp]

No description provided.

[github-actions]

Code Metrics Report

	main (aad5a18)	#18 (afe34cd)	+/-
Coverage	40.4%	57.4%	+17.0%
Code to Test Ratio	1:0.4	1:0.6	+0.1
Test Execution Time	18s	12s	-6s

Details

  |                     | main (aad5a18) | #18 (afe34cd) |  +/-   |
  |---------------------|----------------|---------------|--------|
+ | Coverage            |          40.4% |         57.4% | +17.0% |
  |   Files             |             11 |            11 |      0 |
  |   Lines             |            302 |           216 |    -86 |
+ |   Covered           |            122 |           124 |     +2 |
+ | Code to Test Ratio  |          1:0.4 |         1:0.6 |   +0.1 |
  |   Code              |            784 |           588 |   -196 |
  |   Test              |            328 |           328 |      0 |
+ | Test Execution Time |            18s |           12s |    -6s |

Code coverage of files in pull request scope (30.5% → 49.0%)

Files	Coverage	+/-
cmd/bundler.go	100.0%	+13.5%
cmd/diagnose.go	38.2%	+26.1%
cmd/nodejs.go	90.0%	0.0%
cmd/npm.go	14.3%	+11.5%
cmd/pip.go	14.3%	+11.5%
cmd/pypi.go	83.3%	0.0%
cmd/ruby_gems.go	85.7%	0.0%
cmd/yarn.go	14.3%	+11.5%

---

Reported by octocov