Add saved account auth support

[thromel]

Summary

• Add savedAuths to Profile so clients can retain multiple authenticated accounts.
• Save successful auths and seed the previous active auth when switching from a legacy single-auth profile.
• Preserve non-current saved auths on logout while removing the invalidated current session.

Refs #995

Tests

• DEVELOPER_DIR=/Library/Developer/CommandLineTools cargo fmt --all -- --check
• DEVELOPER_DIR=/Library/Developer/CommandLineTools cargo test
• DEVELOPER_DIR=/Library/Developer/CommandLineTools cargo test -p stremio-core --lib --features derive,analytics -- --test-threads=1
• DEVELOPER_DIR=/Library/Developer/CommandLineTools cargo test -p stremio-core-web -- --test-threads=1
• CARGO_BUILD_JOBS=1 DEVELOPER_DIR=/Library/Developer/CommandLineTools cargo clippy --all --no-deps -- -D warnings
• DEVELOPER_DIR=/Library/Developer/CommandLineTools cargo build

Notes

• This adds core state support for account switching; UI account picker work still needs to consume savedAuths.
• Not run locally: wasm-pack test --chromedriver "$(which chromedriver)" --chrome --headless because local wasm-pack, chromedriver, and Chrome/Chromium CLI are unavailable.

[github-actions]

stremio-core-web prebuild

Prebuild artifact published by the Build workflow for branch issue-995-multiple-logins.

Paste one of these into stremio-web's package.json and run pnpm install to wire this prebuild into a corresponding stremio-web PR:

Release

"@stremio/stremio-core-web": "https://stremio.github.io/stremio-core/stremio-core-web/issue-995-multiple-logins/stremio-stremio-core-web-0.59.0.tgz"

Dev

"@stremio/stremio-core-web": "https://stremio.github.io/stremio-core/stremio-core-web/issue-995-multiple-logins/dev/stremio-stremio-core-web-0.59.0.tgz"