fix: export FeedClient from Python SDK

[nanookclaw]

Summary

Closes #830.

The Python SDK already includes sdks/python/pmxt/feed_client.py, but the package initializer did not expose FeedClient at the top level. This adds the missing import and includes FeedClient in pmxt.__all__, so callers can use from pmxt import FeedClient like the issue requests.

I also extended the existing public-export regression test to assert that FeedClient stays imported from feed_client and listed in __all__.

Verification

• PYTEST_DISABLE_PLUGIN_AUTOLOAD=1 pytest sdks/python/tests/test_public_exports.py
• git diff --check

[realfishsam]

PR Review: VERIFIED

What This Does

Exports FeedClient from the Python SDK's top-level pmxt package so consumers can write from pmxt import FeedClient (or pmxt.FeedClient) without digging into the internal pmxt.feed_client submodule. The companion commit refreshes auto-generated API reference docs to document fetchSeries, UnifiedSeries, and sourceMetadata.

Blast Radius

• Python SDK only (sdks/python/pmxt/__init__.py, sdks/python/tests/test_public_exports.py): two lines of hand-written code
• Auto-generated docs updated: sdks/python/API_REFERENCE.md, sdks/typescript/API_REFERENCE.md, core/api-doc-config.generated.json
• No changes to core/, no exchange logic, no types, no OpenAPI schema, no server, no auth, no router

Consumer Verification

Before (main branch):

from pmxt import FeedClient
# ImportError: cannot import name 'FeedClient' from 'pmxt'

import pmxt; pmxt.FeedClient
# AttributeError: module 'pmxt' has no attribute 'FeedClient'

Verified by AST inspection of sdks/python/pmxt/__init__.py on main: FeedClient absent from both imports and __all__.

After (PR branch):

from pmxt import FeedClient          # works
import pmxt; feed = pmxt.FeedClient('chainlink')  # works

FeedClient is imported from feed_client module and listed in __all__. Both verified via AST inspection on PR branch.

Sidecar health and Polymarket fetchMarkets smoke test confirmed working (success: True, 64742 markets returned) — this PR doesn't touch the sidecar at all.

Test Results

• Build (core TypeScript): PASS
• Core unit tests: PASS — 631/631 (22 test suites)
• Python test_public_exports.py: PASS — 4/4 (including new test_feed_client_is_top_level_public_export)
• Full Python suite: NOT RUN — pmxt_internal generated module not present in repo (build-time artifact); not attributable to this PR
• TypeScript SDK build: NOT RUN — same reason (generated/src/index.js not present)
• E2E smoke (Polymarket): PASS — sidecar returns markets correctly

Findings

1. TypeScript SDK has the same omission (non-blocking, separate issue) — sdks/typescript/pmxt/feed-client.ts exists and is fully implemented, but FeedClient is not exported from sdks/typescript/index.ts. import { FeedClient } from 'pmxtjs' will fail at runtime. The PR title is explicitly scoped to Python, so this is intentional deferral — but worth tracking.
2. api-doc-config.generated.json testDummyMethod → close — the generated docs previously exposed an internal testDummyMethod as a public API entry. The new regeneration correctly shows close() in its place. This is a docs-only fix, not a behavior change.

No blocking findings.

PMXT Pipeline Check

• Field propagation (3-layer): N/A — no type changes
• OpenAPI sync: N/A — no BaseExchange or schema changes
• Financial precision: N/A
• Type safety: OK — FeedClient is a concrete class, no any introduced
• Auth safety: N/A — no credentials touched

Semver Impact

patch — adds a previously missing public export; no existing behavior changed, no API removed

Risk

• TypeScript SDK parity: FeedClient still not exported from pmxtjs. Consumers on the TS side face the same import problem; needs a follow-up PR.
• Full Python integration test suite and TypeScript SDK build could not be run locally (both require generated artifacts not tracked in git). CI is the only gate for those paths.