docs: add fixed window, sliding window log, sliding window counter, and leaky bucket algorithms to redis-py rate limiter page

[YashwinReddy29]

What this adds

Four additional rate limiting algorithm implementations in Python to
the existing redis-py rate limiter page, which currently covers only
the token bucket algorithm.

The other language pages (nodejs, go, java, rust, dotnet, php) also
only cover token bucket. This PR fills that gap for Python.

What's included

• Algorithm comparison table (token bucket, fixed window, sliding
  window log, sliding window counter, leaky bucket)
• Fixed window counter — STRING + Lua, one EVAL round trip
• Sliding window log — SORTED SET + Lua, exact rolling window
• Sliding window counter — STRING x2 + Lua, near-exact with hash
  tags for Redis Cluster compatibility
• Leaky bucket (policing mode) — HASH + Lua, strict no-burst

Clock drift fix

All new scripts derive now from redis.call('TIME') inside the
Lua script rather than time.time() in the caller. This eliminates
clock drift when the limiter runs across multiple application servers.

Full implementation

A complete runnable implementation with demo script is at:
https://github.com/YashwinReddy29/redis-rate-limiting-python

Context

This contribution was suggested by @petyaslavova during review of
redis-py PRs #4248 and #4257, where she pointed to redis/docs as
the right home for application-level rate limiting patterns in Python.

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Note

Low Risk
Documentation-only changes with illustrative Lua/Python snippets; no runtime, auth, or infrastructure behavior is modified.

Overview
Expands the redis-py rate limiter doc beyond token bucket with an algorithm comparison table and four new Lua + Python patterns: fixed window counter, sliding window log, sliding window counter (with hash tags for Cluster), and leaky bucket (policing).

All new examples use redis.call('TIME') in Lua instead of caller-side clocks, and each section notes trade-offs (boundary bursts, memory, estimate accuracy, immediate rejects). Learn more adds a link to the community redis-rate-limiting-python repo.

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[andy-stark-redis]

@YashwinReddy29 Thanks for your contribution!

I've made a few suggestions and there is at least one comment from the Bugbot, which I think you should be able to see now. Please comment on the PR if there is anything you'd like to discuss further.

Once we're happy with this and it's merged, I'll add corresponding examples for the other client languages. This will be a great addition to the docs :-)

[YashwinReddy29]

Thanks for the review! Pushed a commit addressing all the suggestions: fixed the clock-skew issue Bugbot flagged (moved the window/elapsed calculation into the Lua script via redis.call('TIME'), tested locally against real Redis to confirm the fix — 5/5 requests allowed within a window and correct roll-over across window boundaries), renamed the section and folded the comparison table into the intro as suggested, removed the duplicate list, and moved Learn more to the end with the repo link included. Let me know if anything else needs adjusting.

[andy-stark-redis]

LGTM

[andy-stark-redis]

@YashwinReddy29 Excellent - I'll merge this and open a ticket to add the corresponding versions for the other client languages (I can't give a timescale for finishing this, but it should hopefully land quite soon). Thanks once again for your contribution!