feat: Added bounds check for SkBuff::load_bytes and relevant integration test.

[RyanAlameddine]

Alternative to #1187, attempting to resolve the invalid zero-sized read error found on discord and in my personal projects.

This PR contains:

The correct inclusive bounds check.

An integration test which fails before the update and succeeds after.

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This change is 

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[mergify]

@RyanAlameddine, this pull request is now in conflict and requires a rebase.

[dave-tucker]

Reviewed 5 of 5 files at r1, 2 of 2 files at r2.
Reviewable status: 2 of 6 files reviewed, 4 unresolved discussions (waiting on @RyanAlameddine)

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-- commits line 2 at r3:
nit: per the contributing guide this might be better phrased as:

test: Add integration test for SkBuffContext::load_bytes

Adds a  test program `read_one` that triggers a verifier error when
attempting to read one byte from the SkBuffContext.

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-- commits line 5 at r3:
nit. as above:

fix(aya-ebpf): Add bounds check to SkBuff::load_bytes

This resolves the verifier error triggered by the test case added in the previous commit

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-- commits line 8 at r3:
Please remove this commit. Instead, fix the formatting on each commit individually.

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ebpf/aya-ebpf/src/programs/sk_buff.rs line 93 at r3 (raw file):

        let len = len.checked_sub(offset).ok_or(-1)?;
        let len = len.min(dst.len());
        if !check_bounds_signed(len as c_long, 1, dst.len() as c_long) {

This could use a comment. Something like:

// 0 byte reads will trip the verifier. We need to ensure that the valid range of values for len is at least 1.

Also, please cast dst.len() as i64 to match the signature of check_bounds_signed - don't use c_long.