feat: add redis as a backup option

[sighphyre]

Very much a draft to see how complex adding Redis as a backup option would be. 100% vibe coded so almost certainly not prod ready until a human has been in the loop

[coveralls]

Pull Request Test Coverage Report for Build 18684813003

Details

• 34 of 53 (64.15%) changed or added relevant lines in 3 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-1.3%) to 88.629%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/repository/index.ts	1	6	16.67%
src/repository/storage-provider-redis.ts	27	41	65.85%

Totals
Change from base Build 18010500472:	-1.3%
Covered Lines:	1300
Relevant Lines:	1400

---

💛 - Coveralls

[gastonfournier]

We already have an example:

unleash-node-sdk/examples/custom_storage.js

Line 7 in 75b63da

class MyRedisStore {