Fix Xcode 27 activity log section parsing

[fortmarek]

What changed

• Teach ActivityParser to tolerate the extra integer that Xcode 27.0 serializes between an activity log section's subSections array and text field.
• Add a token-level regression test that models the Xcode 27.0 section layout.
• Register the new test in the Linux XCTest manifest.

Why

Xcode 27.0 .xcactivitylog files can fail to parse with:

Unexpected token parsing String: [type: int, value: 0]

The root cause is a serialized format change: section records may include an unknown integer immediately before the text token. Older parser versions read that integer as the text field and fail before any higher-level build parsing can continue.

Impact

Consumers such as Tuist's build analytics processor can parse Xcode 27 build logs instead of rejecting the build payload.

Validation

• swift test --filter ActivityParserTests
• swift test
• .build/debug/xclogparser dump --file '/Users/marekfort/Downloads/xcactivitylog 2/A0007701-F087-4D49-9DB4-DE7A21EB2229.xcactivitylog' --output /private/tmp/xclogparser-xcode27.json