fix: polymarket deprecated endpoint update

[nikbpetrov]

closes #194

No clue actually why the liquidity_num_min param was not used for server-side filtering; it results in more consistent behaviour and 10x fewer requests; i've tested and validated this param and it works as expected; the 5ff64b0 commit adds this (still keeping the client-side filtering for robustness)

fixes a dormant bug where the /markets endpoint can only offset up to 2500, while the qualifying markets are ~1000 more at the moment. Verified with:

> curl -sS -w '\nHTTP %{http_code}\n' \
  'https://gamma-api.polymarket.com/markets?limit=500&active=true&closed=false&archived=false&order=liquidity&ascending=false&offset=2500'
> {"type":"validation error","error":"offset too large, use /markets/keyset for deeper pagination"}

HTTP 422