fix: improve core:network module quality and test coverage

[lihenggui]

Summary

Comprehensive fixes for the core:network module addressing bugs, design issues, and test coverage gaps.

Bug Fixes

• Fix integer division in progress calculation — BinaryFileWriter reported 0% progress until the very end due to Long / Long integer division. Changed to totalBytes.toDouble() / length * 100.0
• Fix response body leak — downloadRules() never closed the OkHttp response body, causing connection pool leaks. Now uses response.use { ... }
• Fix blocking I/O on caller thread — downloadRules() used synchronous .execute() instead of the async .await() coroutine bridge, blocking the caller's thread
• Fix DI-provided Json not being used — RetrofitBlockerNetwork used the global Json default instead of the Hilt-provided instance configured with ignoreUnknownKeys = true

Design Improvements

• Proper error propagation — replaced silent error swallowing (returning empty strings/0) with NetworkException, allowing callers (e.g., SyncWorker) to catch, retry, or surface errors
• Remove unused Retrofit dependency — the module used only OkHttp directly; Retrofit was a dead dependency
• Rename RetrofitBlockerNetwork → OkHttpBlockerNetwork — name now matches the actual implementation
• Remove unused FakeAssetManager from production DI — it was registered in SingletonComponent but never injected anywhere
• Increase buffer size — BinaryFileWriter chunk size from 1KB to 8KB for better throughput
• Update SyncWorker — consolidated error handling to properly catch network exceptions from the new throwing API

Test Coverage

• BinaryFileWriterUnitTest — 7 tests covering: basic write, empty input, multi-chunk large files, progress reporting accuracy, integer division regression, negative length edge case
• OkHttpBlockerNetworkTest — 10 tests covering: GitHub/GitLab JSON parsing, empty/blank/invalid JSON, missing fields, extra fields, multiple commits, blank SHA
• NetworkModelMapperTest — 6 tests covering: full field mapping, null preservation, round-trip conversion for NetworkComponentDetail and NetworkGeneralRule

Test plan

• ./gradlew :core:network:testFossDebugUnitTest — all 23 tests pass
• ./gradlew assembleFossDebug — full build succeeds
• ./gradlew :sync:work:compileFossDebugKotlin — sync module compiles with SyncWorker changes
• ./gradlew :core:network:spotlessCheck — code formatting verified
• ./gradlew :app-compose:dependencyGuardBaseline — baseline updated (Retrofit removed)