Support decimal-second timeout values

[ShudongCai]

Summary

• accept existing integer-second timeout values and canonical decimal-second values with millisecond precision
• pass timeout durations to GNU timeout with an explicit s suffix
• reject malformed explicit timeout values instead of allowing them to weaken the limit
• apply the same timeout contract to the modular runtime and the legacy wrapper

Motivation

Ares2 exposes resource timeouts in milliseconds, while Phobos previously treated the serialized integer as seconds. As a result, a timeout such as 2000 milliseconds could be executed as 2000 seconds.

The coordinated Ares2 change serializes millisecond values as canonical decimal seconds:

• 2000 ms becomes 2.000
• 1234 ms becomes 1.234
• 500 ms becomes 0.500

Phobos accepts that representation and passes it to GNU timeout as 2.000s, 1.234s, or 0.500s.

Compatibility

Existing native Phobos configurations using integer seconds remain valid. Zero and absent timeout values preserve their existing disabled behavior. Existing integer values are not heuristically reinterpreted as milliseconds.

Accepted configuration grammar:

^[0-9]+([.][0-9]{3})?$

Verification

• bash -n core/phobos-common.sh
• bash -n core/phobos-filesystem.sh
• bash -n core/phobos_wrapper.sh
• bash tests/timeout_units.sh
• git diff --check

Coordinated Ares2 change

The corresponding Ares2 serialization change is:

ls1intum/Ares2#175

The updated Phobos runtime must be available before the coordinated Ares2 behavior is released.