fix: avoid argument limit in webauthn base64url encoding

[samsamtrum]

The WebAuthn Base64URL encoder currently spreads the full byte array into String.fromCharCode. Large buffers can exceed the JavaScript argument limit and throw a RangeError before encoding.

This keeps the same byte-to-string conversion, but processes the input in bounded chunks before calling btoa. That avoids passing the entire buffer as function arguments at once while preserving the encoded output.

Verified with a local Node check:

• outputs match the existing implementation for 0, 1, 2, 3, 32, 1024, and 100000 byte buffers
• existing implementation throws RangeError for a 200000 byte buffer
• updated implementation encodes the 200000 byte buffer successfully

I also tried a direct TypeScript check for this file, but the partial dependency install in this workspace is missing several type packages, so that command fails in node_modules type resolution before validating this file.

[Copilot]

Pull request overview

Updates the WebAuthn Base64URL encoder to avoid JavaScript function-argument limits by chunking byte-to-string conversion before calling btoa, preventing RangeError on large ArrayBuffers.

Changes:

• Convert the input ArrayBuffer to a Uint8Array once and encode via chunked String.fromCharCode(...) calls.
• Join chunked strings and pass the result to globalThis.btoa to preserve existing output formatting.

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[joshuascan]

@samsamtrum merging this in now (sorry for the delay!). it will be published shortly as 27.9.1.

[Ethella]

🚀 PR was released in @magic-ext/bitcoin@29.1.1, @magic-ext/cosmos@28.9.1, @magic-ext/evm@1.8.1, @magic-ext/farcaster@5.9.1, @magic-ext/gdkms@16.9.1, @magic-ext/hedera@2.8.1, @magic-ext/oauth2@15.11.1, @magic-ext/passkey@1.4.1, @magic-ext/react-native-bare-oauth@30.10.1, @magic-ext/react-native-expo-oauth@30.10.1, @magic-ext/siwe@3.9.1, @magic-ext/smart-account@1.4.1, @magic-ext/solana@30.9.1, @magic-ext/wallet-kit@0.14.1, @magic-ext/webauthn@27.9.1, @magic-sdk/provider@33.10.1, @magic-sdk/react-native-bare@34.9.1, @magic-sdk/react-native-expo@34.9.1, magic-sdk@33.10.1 🚀