feat: add CLOB_HOST constant for the production endpoint (closes #30)

[Nexory]

Summary

Adds CLOB_HOST = "https://clob.polymarket.com" to py_clob_client_v2/constants.py so consumers do not have to hard-code the production CLOB endpoint in their own code.

The URL is currently duplicated across:

• README.md examples
• every script in examples/
• the test suite (tests/test_client_order_adjustment.py)
• the issue reporter's own code (per Consider adding constant for CLOB host #30)

Closes #30.

Change

CLOB_HOST = "https://clob.polymarket.com"

Added to constants.py alongside the existing ZERO_ADDRESS, POLYGON, AMOY, etc.

Usage

from py_clob_client_v2 import ClobClient
from py_clob_client_v2.constants import CLOB_HOST, POLYGON

client = ClobClient(host=CLOB_HOST, chain_id=POLYGON, key=PK)

Scope

Intentionally minimal — just the production mainnet host. I didn't add an Amoy/testnet host because I don't know whether one is publicly maintained, and a wrong constant would be worse than no constant. Happy to add one in a follow-up if maintainers can confirm the endpoint.

Test plan

• Manual: from py_clob_client_v2.constants import CLOB_HOST works.
• No existing tests changed (purely additive).
• CI passes.

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Note

Low Risk
Single additive constant with no behavior or API changes.

Overview
Adds a shared CLOB_HOST constant (https://clob.polymarket.com) in py_clob_client_v2/constants.py next to existing network constants like POLYGON and AMOY, so callers can pass host=CLOB_HOST to ClobClient instead of repeating the production URL in app code, docs, and examples.

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[Nexory]

Closing in favour of #35, which predates this (2026-04-29) and does the same thing plus exports the constant via __init__.py. Withdrawing.