docs: note that spot_meta_and_asset_ctxs returns two non-parallel lists

[massimiliano1991]

Closes #308.

spot_meta_and_asset_ctxs() returns two lists that are not parallel, and the docstring
lays them out adjacently. This adds a Note: saying so, with the correct pairing. No
behaviour change — docstring only.

The fact, re-measured on mainnet today (2026-08-10)

universe   324 entries
assetCtxs  715 entries
aligned by position :  71
aligned by index    : 324   <- universe[i]["index"]

Why it deserves a line rather than being obvious

Positions 0-70 line up. Everything you are likely to eyeball while testing is inside the
aligned region, so zipping the two lists looks correct and then silently returns a
different asset's prices. The first divergence:

universe[71] = @72 (index 72)   zip -> markPx 1.0   correct -> 0.72847

The perp sibling meta_and_asset_ctxs() is parallel (232 vs 232), so the natural
intuition carries over from perps and is wrong for spot. The SDK already encodes the
distinction in Info.__init__ — perps use enumerate(meta["universe"]), spot uses
spot_info["index"] + 10000 — so the knowledge is in the codebase, just not where a
caller of this method reads.

Reproduce (no keys, no install)

import json, urllib.request
def info(b):
    r = urllib.request.Request("https://api.hyperliquid.xyz/info",
        data=json.dumps(b).encode(), headers={"Content-Type": "application/json"})
    return json.loads(urllib.request.urlopen(r).read())

meta, ctxs = info({"type": "spotMetaAndAssetCtxs"})
uni = meta["universe"]
print(len(uni), len(ctxs))                                                # 324 715
print(sum(1 for i, e in enumerate(uni) if ctxs[i]["coin"] == e["name"]))  #  71  by position
print(sum(1 for e in uni if ctxs[e["index"]]["coin"] == e["name"]))       # 324  by index

Happy to trim the note if it reads long — the pairing line is the part that matters.