Derive COMM segment for MCX futures search and default exact-match off

[PradeepJaiswar]

Problem

On the Search Futures page of the Streamlit interactive examples, searching for MCX commodities
(e.g. CRUDE) returned "No futures found", even though the equivalent API call works:

curl --location
'https://api.upstox.com/v2/instruments/search?query=CRUDE&exchanges=MCX&segments=FUT'
--header 'Accept: application/json'
--header 'Authorization: Bearer <YOUR_ACCESS_TOKEN>'

Root cause

get_futures_sorted() defaulted to segment="FO". The Search Futures and Futures OI Buildup pages
both offer MCX in the exchange dropdown but never passed a segment, so MCX searches ran against FO
and returned nothing. MCX commodities live under the COMM segment.

Changes

• interactive_examples/utils.py — get_futures_sorted() now derives the segment from the exchange
  when not passed explicitly: MCX → COMM, otherwise FO. Explicit segment values (e.g. CURR, COMM)
  are still honored, so existing callers are unaffected. This fixes both affected pages (Search
  Futures and Futures OI Buildup) at the source rather than per call site.
• interactive_examples/streamlit_app.py — "Exact underlying match" checkbox on the Search Futures
  page now defaults to False, so partial queries like CRUDE return CRUDEOIL contracts instead of
  being filtered out.

Testing

• Validated segment derivation logic (MCX → COMM, NSE/BSE → FO) and syntax.
• Manual verification: CRUDE on MCX now returns CRUDEOIL futures contracts.