Validate HDGF v6+ chunk Length before narrowing to int

[metsw24-max]

The HDGF v6+ ChunkHeader parser previously narrowed the unsigned 32-bit Length field using a plain (int) cast:

(int) LittleEndian.getUInt(...)

Values larger than Integer.MAX_VALUE silently wrapped to negative numbers and could propagate into chunk offset arithmetic in ChunkFactory.createChunk(...):

offset + getLength() + sizeInBytes

This patch replaces the v6+ Length cast with Math.toIntExact(...), matching the existing v4/v5 handling already used in the same method.

Identifier-style fields (type, id, unknown1) intentionally retain their existing casts. Existing tests already verify that negative reinterpretation is part of the current behavior contract (for example header.getId() == -1 for 0xFFFFFFFF).

Tests

Added regression coverage for:

• rejecting oversized v6+ Length values (0x80000001)
• continuing to accept Integer.MAX_VALUE as a valid representable length

[pjfanning]

thanks - merged