fix(cam_hal): prevent SOI scan from (1) running on length<3 and (2) over-reading the last 2 bytes

[RubenKelevra]

x## Description

Changes:

• Store SOI as a 3-byte array (0xFF D8 FF) and use sizeof() everywhere.
• Early-exit when length < 3 to avoid over-reading
• calculate end index correctly, to avoid over-reading

Related

In the search for the cause of crashes reported by @turenkomv here: esphome/esphome#8832 (comment) I found this overread of a pointer, which can cause undefined behaviour.

Checklist

Before submitting a Pull Request, please ensure the following:

• 🚨 This PR does not introduce breaking changes.
• All CI checks (GH Actions) pass. (?)
• Documentation is updated as needed.
• Tests are updated or added as necessary.
• Code is well-commented, especially in complex areas.
• Git history is clean — commits are squashed to the minimum necessary.

[RubenKelevra]

@turenkomv thanks for your patience. Sadly this bug can IMHO not cause a stack trashing, only cause wrong returns.

[RubenKelevra]

Log changes moved to PR #765 to keep this PR small.

[RubenKelevra]

Updated to the latest master branch commit

[me-no-dev]

I will merge this next, but first update the branch and do not use sizeof for SOI and EOI. Your other PR will go after that with everything from the previous and this one merged it.

[RubenKelevra]

but first update the branch and do not use sizeof for SOI and EOI.

Thanks for the suggestion, I've changed this.

Should be ready for merge now. :)