fix: bump mpp-rs to accept standard base64 in WWW-Authenticate

[gakonst]

Problem

tempo request fails against servers that encode the request field in the WWW-Authenticate header using standard base64 (RFC 4648 §4) instead of base64url (RFC 4648 §5):

tempo request -t -X POST --json '{"vcpus":1,"ram_mb":256,"disk_gb":1,"duration":60}' https://openvps.sh/v1/provision
# → E_PAYMENT: "Unsupported payment method: "

The misleading error occurs because mpp::parse_www_authenticate fails on the base64-padded request field before ever reading the method field, causing the error to cascade as an empty-string method.

Fix

Bumps mpp dependency to include tempoxyz/mpp-rs#149, which makes base64url_decode lenient — it normalizes standard base64 (+, /, =) to URL-safe alphabet before decoding, matching the mppx TypeScript SDK behavior.

Verified

Before: E_PAYMENT: "Unsupported payment method: "

After (dry-run):

./target/release/tempo-request -t --dry-run -X POST \
  --json '{"vcpus":2,"ram_mb":1024,"disk_gb":10,"duration":3600}' \
  https://openvps.sh/v1/provision
# → [DRY RUN] Signed transaction ready, skipping submission.

All tests pass (make test).

Note

Once mpp-rs#149 is merged to main, this branch ref should be updated from fix/lenient-base64-decode-v0.5 back to main.

[github-actions]

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