[roll] Roll fuchsia [ffx][isolate] Propagate all log config values to isolate

ffx_isolate::Isolate was previously propagating only a few
hardcoded fields (dir, level, target_levels, enabled) to the
isolate's user configuration. This caused other standard log
configurations (such as rotations and rotate_size) in the parent
environment to be ignored by the isolate.

This change dynamically propagates the entire parent "log" config
subtree, overriding only the isolate-specific log directory and
forcing logs to be enabled. This ensures that any custom log
configurations are preserved in the isolate.

We also add a unit test to verify this behavior.

Original-Original-Fixed: 396473745
Test: fx test ffx_isolate_lib_test
TAG=agy
CONV=415d7445-26fa-4d87-8f32-a8ad9e8b8c71

Original-Original-Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/1665496
Original-Original-Revision: bc555dd3ef3f2d3f80b80ca3c734a3150268b553
GitOrigin-RevId: e15cc5dca81181a266368ca07f9c79580b8ccd8b
Change-Id: If66cf9dabc56bb208c10fd0c0370bf7ac4a18c54
Reviewed-on: https://fuchsia-review.googlesource.com/c/integration/+/1672874
Cr-Commit-Position: refs/heads/main@{#195288}