Resolve clippy collapsible_if findings in multiple modules

[sergio-ivanuzzo]

Motivation

• Address code-scanning warnings from clippy about collapsible nested if/if let patterns in input handling and buffered message retrieval to improve code clarity and satisfy lint rules.

Description

• Refactored JsonNavigator Up/Down handlers to combine nested if checks into a single condition while preserving the moved flag and scroll behavior (src/plugins/tui/components/json_navigator/mod.rs).
• Collapsed sequential checks for reading and parsing a user input line into a chained if let to simplify the interactive choice flow (src/plugins/dbg_ui/mod.rs).
• Combined nested if let checks in OrderedReceiver::recv into a chained if let to simplify buffered entry retrieval (src/client/types.rs).

Testing

• Ran cargo fmt --all and cargo fmt --all -- --check successfully with no formatting issues.
• Attempted cargo clippy --all-targets --all-features -q, but the run failed due to an environment network error when downloading https://index.crates.io/config.json (HTTP 403 via CONNECT tunnel), so clippy could not be fully validated.
• Verified local formatting and non-network validation steps completed without errors.

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Codex Task