🧹 Refactor GraphStatsCollector to improve code health

[tstapler]

🎯 What: Moved JournalEntry, pageNameFromFile, scan, connectivity, histogram, and epochDay from local functions inside collect to private members of GraphStatsCollector.
💡 Why: Reduces the length and nesting complexity of the collect function, improving code readability and maintainability.
✅ Verification: Verified that compilation passes and there were no syntax errors. Since no tests explicitly cover this file in jvmTest, ensured the core build works.
✨ Result: The collect function is now much cleaner, focusing only on the high-level logic, with detail implementations separated into private helper methods.

---

PR created automatically by Jules for task 6461131231550887623 started by @tstapler

[google-labs-jules]

👋 Jules, reporting for duty! I'm here to lend a hand with this pull request.

When you start a review, I'll add a 👀 emoji to each comment to let you know I've read it. I'll focus on feedback directed at me and will do my best to stay out of conversations between you and other bots or reviewers to keep the noise down.

I'll push a commit with your requested changes shortly after. Please note there might be a delay between these steps, but rest assured I'm on the job!

For more direct control, you can switch me to Reactive Mode. When this mode is on, I will only act on comments where you specifically mention me with @jules. You can find this option in the Pull Request section of your global Jules UI settings. You can always switch back!

New to Jules? Learn more at jules.google/docs.

---

For security, I will only act on instructions from the user who triggered this task.

[github-actions]

Android Load Benchmark

Instrumented benchmark on an API 30 x86_64 emulator — 500-page synthetic graph.

Comparing decdd4ba (this PR) vs dc94048f (baseline)
Device: API 30 x86_64 emulator — 530 pages loaded

Graph Load

Metric	This PR	Baseline	Delta
Phase 1 TTI ↓	35ms	35ms	0 (0%)
Phase 3 index ↓	3813ms	3572ms	+241ms (+7%) ⚠️

Interactive Write Latency (during Phase 3)

Metric	This PR	Baseline	Delta
Write p95 (baseline) ↓	16ms	8ms	+8ms (+100%) ⚠️
Write p95 (during phase 3) ↓	19ms	14ms	+5ms (+36%) ⚠️
Jank factor ↓	1.19x	1.75x	-0.56x (-32%) ✅
Concurrent writes ↑	18	18	0 (0%)

SAF I/O Overhead (ContentProvider vs direct File read)

Measures Binder IPC cost added by ContentResolver per readFile() call.
Real SAF via ExternalStorageProvider will be higher on device; this is a lower bound.

Metric	This PR	Baseline	Delta
Direct read / file ↓	0.0ms	0.0ms	0 (0%)
Provider read / file ↓	0.2ms	0.2ms	0 (0%)
IPC overhead ratio ↓	6x	6x	0 (0%)
↓ lower is better · ↑ higher is better

[github-actions]

JVM Load Benchmark (Desktop)

Synthetic in-memory benchmark measuring load performance for the desktop (JVM) app.
Comparing decdd4ba (this PR) vs dc94048f (baseline)
Graph config: xlarge — 230 pages

Metric	This PR	Baseline	Delta
Phase 1 TTI ↓	7ms	1ms	+6ms (+600%) ⚠️
Phase 2 background ↓	1ms	0ms	+1ms ⚠️
Phase 3 index ↓	2ms	1ms	+1ms (+100%) ⚠️
Total ↓	10ms	2ms	+8ms (+400%) ⚠️
Write p95 (baseline) ↓	18ms	17ms	+1ms (+6%) ⚠️
Write p95 (under load) ↓	1ms	n/a
Jank factor ↓	0.06x	n/a
↓ lower is better

Flamegraphs (this PR)

**Allocation** — object allocation pressure (JDBC/SQLite churn)

Alloc flamegraph not available

CPU — method-level hotspots by on-CPU time

CPU flamegraph not available

Top allocation hotspots (this PR)

`36.3%` byte[]_[k] `7.4%` java.lang.String_[k] `7.1%` java.util.LinkedHashMap$Entry_[k] `5.5%` int[]_[k] `3.8%` java.lang.Object[]_[k]

Top CPU hotspots (this PR)

`96.9%` /usr/lib/x86_64-linux-gnu/libc.so.6 `1.1%` /tmp/sqlite-3.51.3.0-39397742-94e6-4038-8f36-7eeb6a891fbe-libsqlitejdbc.so `0.4%` __libc_pwrite `0.3%` fsync `0.2%` SR_handler