[roll] Roll fuchsia [audio_core] mix range checks and object lifetimes

Improve boundary checks, integer arithmetic precision, and object
ownership across audio mixing, DSP sampling, and effect loading
pipelines. Specifically:

- Mixer / MixStage: Cap destination frame count in Mixer::Mix during
  gain ramping to *dest.frame_offset_ptr + kScaleArrLen (960 frames),
  ensuring that sampling operations remain strictly within the
  allocated scale_arr buffer during large mix requests (b/521640280).
- MixStage: Widen block size calculation in MixStage::MixStage from
  32-bit integer multiplication to size_t (b/521640620), preventing
  arithmetic overflow when sizing multi-channel output buffers.
- Sampler: Adjust signed modulo remainder and quotient division in
  Sampler::State::AdvancePositionsBy when dest_frames is negative
  (b/525551854), ensuring source_pos_modulo_ always remains positive and
  strictly less than step_size_denominator_.
- EffectV1: Store instance_name_ as an owning std::string instead of a
  non-owning std::string_view (b/521640738), guaranteeing string
  validity across pipeline reconfigurations and extended lifetimes.

New and updated unit test cases:
- MixStageTest.RampingMixExceedsScaleArrLen
- DynamicRange.RampingMixExceedsScaleArrLen
- MixStageTest.BlockSizeMultiplication
- SamplerStatePositionTest.AdvancePositionsNegativeDestFrames
- EffectV1Test.InstanceNameLifetime

Original-Original-Fixed: 521640280
Original-Original-Fixed: 521640620
Original-Original-Fixed: 525551854
Original-Original-Fixed: 521640738
Test: fx test audio_core_unittests
Test: fx test audio_lib_processing_unittests
Test: fx test audio_effects_loader_unittests
Original-Original-Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/1685895
Original-Original-Revision: 3936fdff9d305a7ea40c7379a0f7c41512e87f7a
GitOrigin-RevId: e44ed6558e4cd15ff7f9e6fd71f371e1a739304c
Change-Id: I11fc72a875105ed365412b1cd4b6495e3ee7291e
Reviewed-on: https://fuchsia-review.googlesource.com/c/integration/+/1689956
Cr-Commit-Position: refs/heads/main@{#196022}