Fix rustup-init fallback: wrap in ErrorActionPreference Continue

[Finesssee]

Summary

• wrap rustup-init.exe invocation in try/finally with $ErrorActionPreference = 'Continue' — the script default is Stop, and rustup-init writes warnings to stderr (e.g. "It looks like you have an existing installation of Rust at:") which triggered an immediate throw under Stop
• add --no-modify-path flag to avoid PATH conflicts with existing Chocolatey Rust installation

Root cause

Pipeline #35: choco install rustup.install failed (package not found on community feed), then rustup-init.exe fallback triggered but failed because rustup-init wrote a warning to stderr about the existing Rust installation. With $ErrorActionPreference = Stop at the script level, the stderr warning was treated as a terminating error, throwing before rustup-init could complete.

Validation

• PowerShell parser passed for all release scripts
• scripts/release-pipeline.tests.ps1 passed
• circleci config validate .circleci/config.yml passed
• no version files changed

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