extranonce mgmt - heap mgmt Update mining.c

[JustANewbie1]

Key Optimizations:

• Extranonce management: The extranonce_2_generate function now avoids heap allocation by using pre-allocated buffers, improving memory efficiency. Midstate handling: The code minimizes copying and memory usage by directly working with buffers when possible. Efficient hashing: Instead of recalculating the entire block header, the midstate is used, reducing the computational load on the system.
• Simplified dynamic memory usage: Dynamic memory allocations are kept to a minimum, with most operations handled via stack-allocated buffers where feasible.

[JustANewbie1]

tried to improve 2-3 things here too

[JustANewbie1]

need to fix previous pr first