feat: Adding method for confirming login

[kysely]

This PR adds method for confirming passwordless login.

Previously, the confirmation was done in Air using this client's fetch. I'm moving the feature as a dedicated confirmation method here because the view of service-client shifted since then to be more capable service SDK (rather than a thin wrapper over fetch). It might also be better reused among other passwordless login methods in service client.

At the same time, this fixes the issue present in Air implementation where e-mail passed to confirmation was not correctly URI-encoded.

• [x] add confirmPasswordlessLogin method (move from Air)
• [x] fix email URI encoding

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[kysely]

Good catch, thanks!

• It turned out few other tests had inconsistent names & expectation descriptions, so I straightened them all up.
• Also worked in the linter improvement hints