Fix broken Nifty Indices fetchers (index_history, index_pe_pb_div, index_total_returns) after API migration

[0xmohitsen]

Problem

index_history, index_pe_pb_div, and index_total_returns fail with JSONDecodeError / KeyError: 'd' because niftyindices.com changed its API.

Old (broken):

• URL: https://niftyindices.com/Backpage.aspx/...
• Response: {"d": "[...]"}
• No session cookies

New (working):

• URL: https://www.niftyindices.com/BackPage/...
• Response: direct JSON array
• Session warmup required for ASP.NET_SessionId / Akamai cookies

Fix

• Update niftyindices_headers (Chrome 150, www.niftyindices.com)
• Add session warmup before POST
• Parse both old {"d": "..."} and new direct-array responses
• Raise a clear error when HTML is returned instead of JSON

Affected functions

• index_history
• index_pe_pb_div
• index_total_returns

Tested

from nsepython import index_total_returns
df = index_total_returns("NIFTY 500", "26-Jul-2026", "29-Jul-2026")
print(df.head())  # returns valid DataFrame