Return EOF when reading past the end of a memory archive

[rodrigouroz]

Changes proposed in this PR

Reading a memory-backed archive whose local-file-header offset points past the end of its data currently traps while constructing a range in MemoryFile.readData. Return zero bytes at or beyond EOF before computing that range, matching the file-backed reader's behavior.

Add regression tests for EOF reads on empty, ordinary, and sliced Data, preserving the file position and allowing a seek back to valid data. Also exercise a malformed local-header offset through Archive(data:accessMode:) and register both tests in the Linux test list.

Tests performed

• Both new tests terminate with signal 5 on the base revision and pass with the fix.
• Full release suite: 133 tests passed on macOS 27.0, Xcode 27.0, Swift 6.4.
• Line coverage remains 100% (2,320/2,320), using the CI coverage exclusions. Archive+MemoryFile.swift also has 100% line coverage.
• SwiftLint 0.65.1: no violations across all 50 tracked Swift files.
• A standalone consumer reproducing VoxKey's malformed ZIP import now completes without a crash; valid ZIP contents remain readable.
• git diff --check passes. Linux was not run locally.

Further info for the reviewer

This came from VoxKey's vocabulary archive import, which currently uses a temporary file to avoid this memory-reader trap.

Seeking past EOF remains permitted, including for existing write behavior. Invalid archive entries still terminate iteration as before; this change does not add archive validation or change the public API. Two blank lines were removed from the test registry file to keep it within the existing 400-line SwiftLint limit.

Prepared with AI assistance; the regression and consumer checks above were run locally.

Open Issues

No matching open issue was found. Base revision: e7a17d57c583067eaa6659cd6d9521265b7664e9.