fix: count single-nonzero PR milestones correctly

[kitsuyui]

Summary

• add a rarity helper that counts every built-in ^[1-9]0+$ pull request milestone up to the current PR number
• use that count for pr_reaches_contain_only_one_nonzero_digit rarity gating while keeping the existing power-of-ten helper intact
• add regression coverage and refresh the checked-in dist/ output

Verification

• bun install --frozen-lockfile
• bun run format
• bun run lint
• bun run test
• bun run build
• git diff --exit-code -- dist
• bunx madge --circular src

[github-actions]

gh-counter

PR gate

	Removed	Added	+/-
TODO/FIXME	0	0	0

Repo dashboard

	main (d8fc92c)	#832 (326a6df)	+/-
TODO/FIXME	0	0	0

---

Reported by gh-counter

[github-actions]

🎉 Happy commit!

• dogfooding: PR fix: count single-nonzero PR milestones correctly #832 always celebrates.
• dogfooding: e31a0ebdba47cbcc54409594c38bfbc9d8c2d0d6 always celebrates.

[github-actions]

Code Metrics Report

	main (d8fc92c)	#832 (326a6df)	+/-
Coverage	99.0%	99.1%	+0.0%
Code to Test Ratio	1:0.5	1:0.5	+0.0
Test Execution Time	1s	1s	0s

Details

  |                     | main (d8fc92c) | #832 (326a6df) |  +/-  |
  |---------------------|----------------|----------------|-------|
+ | Coverage            |          99.0% |          99.1% | +0.0% |
  |   Files             |              5 |              5 |     0 |
  |   Lines             |            107 |            113 |    +6 |
+ |   Covered           |            106 |            112 |    +6 |
+ | Code to Test Ratio  |          1:0.5 |          1:0.5 |  +0.0 |
  |   Code              |           1438 |           1483 |   +45 |
+ |   Test              |            777 |            811 |   +34 |
  | Test Execution Time |             1s |             1s |    0s |

Code coverage of files in pull request scope (100.0% → 100.0%)

Files	Coverage	+/-	Status
src/rarity.ts	100.0%	0.0%	modified
src/rules.ts	100.0%	0.0%	modified

---

Reported by octocov

[github-actions]

gh-build-size

Target	main	#832	+/-
Total action artifacts	23,291,895 B	23,296,278 B	+4,383 B
Runtime bundle	1,152,247 B	1,153,157 B	+910 B
Source maps	17,124,104 B	17,127,463 B	+3,359 B
Type declarations	4,973,475 B	4,973,589 B	+114 B

---

Reported by gh-build-size