chore: removed ping in favor of keepalive

[pubalokta]

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Description

We observed that limitd-redis fails to promptly detect a stale TCP connection to Redis, only realizing the connection is down after approximately 12 minutes. After this delay, it reconnects as expected.

This update enables the keepAlive feature in ioredis, which sets the KEEPALIVE option on the socket. This allows for a quicker reaction to stale connections.

Key changes:

• The keepAlive feature is enabled by default and set to 10000 ms.
• The keepAlive interval can be customized by passing the keepAlive argument to the LimitdRedis constructor.
• Setting the keepAlive argument to a non-numeric value will disable the feature.
• The manually-implemented ping mechanism against Redis has been removed, as we now rely on ioredis' keepAlive feature.

Testing

Describe how this can be tested by reviewers. Be specific about anything not tested and reasons why. If this library has unit and/or integration testing, tests should be added for new functionality and existing tests should complete without errors.

Please include any manual steps for testing end-to-end or functionality not covered by unit/integration tests.

Also include details of the environment this PR was developed in (language/platform/browser version).

• This change adds test coverage for new/changed/fixed functionality

• Using the previous limitd-redis version:

Welcome to Node.js v18.20.2.
Type ".help" for more information.
> const LimitdRedis = require("limitd-redis");
undefined
> client = new LimitdRedis({uri:'localhost:6379', buckets:{}});
> process.pid
49290

$ lsof -a -p 49290 -i 4 -T f                               
COMMAND   PID       USER   FD   TYPE  DEVICE SIZE/OFF NODE NAME
node    49290       ****   25u  IPv4    ****      0t0  TCP localhost:58196->localhost:6379 (SO=KEEPALIVE=7215075...)

• Using the new version - default value

Welcome to Node.js v18.20.2.
Type ".help" for more information.
> const LimitdRedis = require("limitd-redis");
undefined
> client = new LimitdRedis({uri:'localhost:6379', buckets:{}});
> process.pid
49290

lsof -a -p 51327 -i 4 -T f   
COMMAND   PID  USER   FD   TYPE  DEVICE SIZE/OFF NODE NAME
node    51327   ***   26u  IPv4     ***      0t0  TCP localhost:59435->localhost:6379 (SO=KEEPALIVE=10000...)

• Using the new version - custom value

Welcome to Node.js v18.20.2.
Type ".help" for more information.
> const LimitdRedis = require("limitd-redis");
undefined
> client = new LimitdRedis({uri:'localhost:6379', buckets:{}, keepAlive: 5000});
> process.pid
54298

lsof -a -p 54298 -i 4 -T f
COMMAND   PID   USER   FD   TYPE  DEVICE SIZE/OFF NODE NAME
node    54298   ****   26u  IPv4    ****      0t0  TCP localhost:61643->localhost:6379 (SO=KEEPALIVE=5000....)

Checklist

• I have added documentation for new/changed functionality in this PR or in auth0.com/docs
• All active GitHub checks for tests, formatting, and security are passing
• The correct base branch is being used, if not the default branch

[pubalokta]

added to be able to distinguish between local and CI, for customizing the environment if needed

[kampde]

not entirely sure if github doesn't add it themselves, but good anyway.