Optimize ptrace functions

[giulianobelinassi]

Ptracing is slow. Therefore, we should avoid calling it constantly. Some ideas to optimize it are:

• Use caching on read_bytes to avoid calling ptrace again on already-read elements.
• Avoid calling read_bytes only to find string length.
• When reading/writing memory, write the size of a long as much as it can.
• Reduce sleep time on attach.

Others, but related:

• Cache dynsym and synstr on get_loaded_symbol_addr
• Rely on disk images if build id matches.