fix: explicit slice coercion in MotionPhoto attribute comparison

[Enduriel]

Problem

cargo clippy/cargo build fails in src/jpeg.rs when rkyv is present
elsewhere in the dependency graph:

error[E0277]: can't compare `Option<&[u8]>` with `Option<&[u8; 11]>`
error[E0277]: can't compare `Option<&[u8]>` with `Option<&[u8; 9]>`

extract_attr_value() returns Option<&[u8]>, while the literals Some(b"MotionPhoto") and Some(b"video/mp4") are Option<&[u8; N]>. The comparison normally works because Rust coerces
the array reference to a slice — but that coercion only fires when the target type is unambiguous.

rkyv's blanket impl

impl<T: PartialEq<U>, U> PartialEq<ArchivedOption<T>> for Option<U>

adds another PartialEq candidate, so coercion no longer applies and the literal stays &[u8; N], for which no matching impl exists.

Fix

Coerce the literals to slices explicitly:

extract_attr_value(tag, b"Item:Semantic") == Some(&b"MotionPhoto"[..])
extract_attr_value(tag, b"Item:Mime")     == Some(&b"video/mp4"[..])

This makes the comparison type-correct on its own, independent of any other crate in the graph.

Notes

• No behavior change; purely a type-annotation fix.
• Reproducible by adding rkyv as a dependency to a crate that also uses this one.

[mindeng]

LGTM. Clean fix — the explicit slice coercion resolves the rkyv blanket impl ambiguity without any behavior change. Tests (366 passed) and clippy are clean.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.84%. Comparing base (12de899) to head (b428e9b).
⚠️ Report is 9 commits behind head on main.

Files with missing lines	Patch %	Lines
src/jpeg.rs	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #58      +/-   ##
==========================================
- Coverage   90.33%   89.84%   -0.49%     
==========================================
  Files          38       38              
  Lines        8212     8399     +187     
==========================================
+ Hits         7418     7546     +128     
- Misses        794      853      +59     

Flag	Coverage Δ
nom-exif	89.84% <0.00%> (-0.49%)	⬇️

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