Replace per-process in-memory cache with Flask-Caching (Redis backend)

[Copilot]

SimpleCache via a plain dict is per-process. With 4 Gunicorn workers each maintains its own cache — 4× API load, inconsistent state across requests.

Changes

• app.py: Replace _cache dict + manual TTL logic with flask_caching.Cache. Backend configurable via CACHE_TYPE / CACHE_REDIS_URL env vars; defaults to SimpleCache for single-worker/dev use.
• docker-compose.yml: Add redis:7-alpine service; wire nautobot-maps to use RedisCache by default.
• requirements.txt: Add Flask-Caching==2.3.1, redis==5.3.0.
• .env.example / README.md: Document CACHE_TYPE and CACHE_REDIS_URL.
• Tests: _cache.clear() → cache.clear(); rewrite expiry test to use Flask-Caching timeout instead of manipulating internal dict timestamps.

Usage

# .env
CACHE_TYPE=RedisCache
CACHE_REDIS_URL=redis://redis:6379/0

No env vars needed for dev — falls back to SimpleCache automatically.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Issue: Fix the in-memory cache — it breaks with multiple workers</issue_title>
<issue_description>Flask-Caching's SimpleCache is per-process. With 4 Gunicorn workers, each has its own cache — you get 4x the Nautobot API load and inconsistent state. Add Redis:
yaml# docker-compose.yml additions
redis:
image: redis:7-alpine
restart: unless-stopped

Add to `.env`:

CACHE_TYPE=RedisCache
CACHE_REDIS_URL=redis://redis:6379/0
Wire it in app.py via Flask-Caching config.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Issue: Fix the in-memory cache — it breaks with multiple workers #47

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