Fix max-content width of inline boxes following a mandatory break

[nicoburns]

LLM Contributions: This PR (code, test, and description) was produced by Devin, an AI agent, at nicoburns' request.

calculate_content_widths detected a mandatory line break via the Boundary::Mandatory flag on the text atom after the break. Any inline boxes located between the newline character and that atom had already been accumulated into running_max_width by then, so their widths were attributed to the line before the break — under-reporting the max-content width of the line they actually end up on.

This is the root cause of DioxusLabs/blitz#705: inline-block links following a <br> wrapped inside a shrink-to-fit container on https://freyaui.dev even though they fit on one line (Blitz sized the container from parley's under-reported max-content width).

The fix mirrors the line breaker's behavior directly in calculate_content_widths: when an atom is a Whitespace::Newline, the current line is finalized immediately (for both min- and max-content accumulators) and the newline contributes no advance — matching break_all_lines, where a newline ends the line right after itself and everything following it (including inline boxes) belongs to the next line. The Boundary::Mandatory flag on the following atom now only acts as a soft break opportunity for the min-content width.

Includes a regression test (inline_boxes_after_newline_max_content_width) with a newline followed by three inline boxes; it fails on main (layout broken at the reported max-content width comes out wider than that width, i.e. boxes wrap) and passes with this change.

Changelog

Fixed

• Inline boxes directly following a mandatory line break now contribute to the max-content width of the line they end up on.

Link to Devin session: https://dioxus.staging.devinenterprise.com/sessions/5da2da1c45d24bd89a90d920fd698681
Requested by: @nicoburns

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