feat: add task analytics storage

[saurabhhhcodes]

Summary

• adds dependency-free in-memory TaskAnalytics storage for smart-routing classifications
• records task type, confidence, model/provider, latency, success state, timestamp, and metadata
• exposes getAnalytics() summaries with task counts, model/provider usage, averages, success/failure counts, and bounded recent events
• exports the analytics class and default singleton from the package entrypoint

Closes #25

Validation

• npm ci
• npm run build
• node tests/task-analytics.test.js
• node tests/cross-provider.test.js
• git diff --check

[saurabhhhcodes]

Quick review/scoring follow-up: this PR is mergeable/clean from GitHub’s side and implements linked issue #25.

Validation already listed in the PR body:

• npm ci
• npm run build
• node tests/task-analytics.test.js
• node tests/cross-provider.test.js
• git diff --check

Could you please review when available and mirror the GSSoC labels from #25 onto the PR before merge: GSSoC 2026, level2, smart-routing feature, and suitable type/quality labels? The PR currently has no visible scoring labels.