fix: Replaced os.popen() with Python's inbuilt file handling

[S1DDHEY]

Description

Problem or Issue being addressed

Resolves #856

In tools_views.py, the entropy generation logic uses os.popen("cat /proc/cpuinfo | grep Serial") to gather the CPU serial number for mixing into the seed entropy hash. os.popen() implicitly spawns a shell, which is unnecessary here since the data can be read directly via Python's built-in file I/O.

Solution

Replaced the os.popen() call with native Python file I/O using open("/proc/cpuinfo", "r"). This reads the file line by line and extracts the Serial field without spawning any external processes (cat, grep) or a shell.

Also removed the now-unused import os at the top of the file, as no other code in the file depends on it.

Additional Information

• The new implementation selects the first Serial entry (via break), whereas the previous os.popen approach would effectively select the last one. In practice, cpuinfo contains only a single Serial field, so the behavior is equivalent on all current hardware.
• The existing try/except block is preserved, so on non-Raspberry Pi hardware (or any system without cpuinfo), the code gracefully falls back to hash_bytes = b'0' as before.
• os.popen() is not strictly deprecated but is discouraged in favor of subprocess.run() or native file I/O. Since we're simply reading a local file, native file I/O is the simplest and most direct approach — no shell or subprocess needed.

Screenshots

N/A

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This pull request is categorized as a:

• New feature
• Bug fix
• Code refactor
• Documentation
• Other

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Checklist

I ran pytest locally

• All tests passed before submitting the PR
• I couldn't run the tests
• N/A

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I included screenshots of any new or modified screens

Should be part of the PR description above.

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• No
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I added or updated tests

Any new or altered functionality should be covered in a unit test. Any new or updated sequences require FlowTests.

• Yes
• No, I’m a fool
• N/A

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I tested this PR hands-on on the following platform(s):

• Raspberry Pi OS Manual Build
• SeedSigner OS on a Pi0/Pi0W board
• Emulator

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[PROWLERx15]

This appears to be a straightforward cleanup to me.

Reading /proc/cpuinfo directly is simpler and more appropriate than shelling out to cat | grep for this.

I do not see any obvious issue with the change. Main thing worth confirming is the equivalence on Rasp Pi, but the approach itself looks good.