Fix MEGA ug/usl response compatibility

[mjc]

Summary

Fix two response compatibility issues against MEGA's current API / SDK behavior:

• ug / user info: accept empty optional user attributes instead of treating them as populated values
• usl / list sessions: accept MEGA's positional session-array response shape

What changed

ug / user info

• treat empty optional base64-encoded attributes as missing
• correctly handle empty country, birthday, birthmonth, and birthyear
• keep partial or invalid birth-date data from producing a bogus date
• move user-info response conversion into a dedicated typed conversion with small internal decoding helpers

usl / list sessions

• deserialize MEGA's positional session rows
• tolerate null/empty textual fields the way the MEGA SDK does
• preserve object-shape fallback compatibility
• reduce parser overhead while keeping behavior the same

Tests

Added SDK-linked regression coverage for:

• ug protocol parsing and public UserInfo mapping
• usl protocol parsing and public SessionInfo mapping
• empty optional attrs
• partial / invalid birth-date cases
• 6 / 8 / 9-field session row shapes
• null text fields
• invalid session row lengths

The new tests include links back to the corresponding meganz/sdk parser code used as the source of truth.

Why

MEGA's real response shapes are more permissive than mega-rs previously assumed in these two endpoints. This change makes mega-rs accept valid MEGA output instead of failing on empty optional user-info attrs or positional session responses.

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Adds a dedicated UserInfo module and improves protocol parsing to better match MEGA’s SDK behavior, with regression tests covering edge cases.

Changes:

• Introduces src/user_info with base64 decoding helpers and a UserInfo model implementing TryFrom<UserInfoResponse>.
• Refactors Client::user_info to use the new UserInfo conversion and re-exports UserInfo from the crate.
• Implements a custom Deserialize for protocol::commands::SessionInfo to accept multiple wire shapes (object and positional arrays), plus adds regression tests.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
src/user_info/decoding.rs	Adds shared base64 decoding utilities for required/optional fields and numeric parsing.
src/user_info.rs	Introduces UserInfo and conversion logic from the protocol response, with tests.
src/sessions.rs	Adds tests verifying SessionInfo mapping from protocol session info.
src/protocol/commands.rs	Adds flexible SessionInfo deserialization and extensive regression tests for response shapes.
src/lib.rs	Wires in the new user_info module, re-exports UserInfo, and refactors Client::user_info.

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[mjc]

This one is a false positive: in match responses.as_slice() { [Response::UserInfo(response)] => response, ... }, response is already borrowed from the slice, so UserInfo::try_from(response) is passing &UserInfoResponse as intended.