fix: security, correctness, and performance improvements from TODO review

[Copilot]

• C1: readUint32LE signed overflow — already fixed (>>> 0)
• C2: PNG readUint32 signed overflow — already fixed (>>> 0)
• C3: LZW push(...entry) stack overflow — already fixed (for-of loop)
• H4: WebP local readUint32LE duplicate — already fixed (imports from byte_utils)
• H1: TIFF double-compression — cache compressedFrames[] in first pass, reuse .length for StripByteCounts
• H2: ICO non-integer actualHeight — use Math.floor before validateImageDimensions
• H3: PNG decode loop missing bounds check — add if (pos + 8 > data.length) break
• M1: PCX missing validateImageDimensions — added after dimension calculation
• M2: BMP extractMetadata uses readUint32LE for signed DPI fields — changed to readInt32LE
• M3: JPEG IDCT precompute cosine table — IDCT_COS[k][n] module-level constant, ~10-100× faster on large images
• M4: medianFilter allocates 4 arrays per pixel — moved outside loop, reset length = 0 per iteration
• M7: Misleading comment on hue-rotation normalization — updated to "0–360 range"
• CI fix: deno fmt CHANGELOG.md line-wrap

[Hexagon]

@copilot have a look at the ci fsilures

[Copilot]

@copilot have a look at the ci fsilures

Fixed in 1ad7b76 — deno fmt --check was failing because a CHANGELOG.md line wrapped at the wrong column. Applied deno fmt to correct the wrapping.