fix: mitmdump process leaked and respawned on every dynamic analysis run

[alanhasn]

Closes #2543

Root cause

mobsf_agents_setup() in environment.py called create_ca() unconditionally on every dynamic analysis session. create_ca() spawns a detached mitmdump -n process to generate the CA cert, but:

1. It was called even when the CA cert file already existed, spawning a redundant new mitmdump process on every single run.
2. The spawned process was never stopped — it's fully detached (close_fds=True, no stdin/stdout/stderr), so it stayed running forever after the session ended.

This matches the reported behavior: a new mitmdump process appears every time Dynamic Analysis starts, and it never exits after stopping the analysis.

Fix

• create_ca() now waits (polling, up to ~15s) for the CA cert file to actually appear, then calls proc.terminate() on the mitmdump process it started, since it's only needed transiently to generate the cert.
• Removed the unconditional create_ca() call in mobsf_agents_setup(). install_mobsf_ca('install'), called right after, already goes through get_ca_file(), which only generates the CA if it doesn't already exist. The unconditional call was redundant and was the source of the "new process every run" behavior.

Testing

• python -m py_compile on both changed files.
• flake8 on both changed files — clean.
• Manually traced all call sites of create_ca() / get_ca_file() to confirm no other code path relies on the old unconditional-spawn behavior.