Add cargo bin to PATH after rustup-init fallback

[Finesssee]

Summary

• after rustup-init.exe installs rustup to ~/.cargo/bin, explicitly add that directory to PATH via Add-PrerequisitePath before Refresh-PrerequisitePath
• --no-modify-path flag (added in PR Fix rustup-init fallback: wrap in ErrorActionPreference Continue #320) prevents rustup-init from modifying PATH env vars, so the install directory was never on PATH when Require-PrerequisiteCommand checked for rustup

Root cause

Pipeline #36: choco install rustup.install failed 3x (504 Gateway Timeout from Chocolatey community feed). The rustup-init.exe fallback ran but rustup was still not found on PATH because --no-modify-path prevented the install directory from being added to PATH, and Refresh-PrerequisitePath only refreshes from existing Machine+User PATH env vars.

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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