fix(AccountInfoDisplay): culture-safe PnL coloring + render cleanup

[AlbertoAmadorBelchistim]

Summary

Three small, independent changes to AccountInfoDisplay's render path:

1. Bug fix - PnL coloring failed on cultures where , is the decimal separator (es-ES, fr-FR, de-DE, ...) for any PnL ≥ 1000 absolute.
   The old ExtractNumericValue formatted with N2 then re-parsed after stripping commas, which produced an invalid thousand-grouping in those cultures and the parse silently returned 0 — collapsing positive and negative PnL into the neutral colour.

2. Perf - the border RenderPen was instantiated on every OnRender call. Cached as a field.

3. Cleanup

• _stringFormat was constructed but never passed to any DrawString. Removed.
• Padding promoted to private const.
• The Container?.Region == null guard made explicit (Region is a struct, so the null-conditional only checks Container).

No public API changes.

Commits

• fix(account-info): culture-safe value coloring
• perf(account-info): cache border RenderPen across renders
• chore(account-info): drop dead RenderStringFormat field; tighten guard

Notes

• Total PnL continues to use OpenPnL + ClosedPnL (session-level) rather than Portfolio.TotalPnL (cumulative). This is intentional and now documented inline in BuildLines.
• RenderFont and RenderPen are sealed and do not implement IDisposable in the SDK, so no explicit disposal is required when references are replaced.

Verification

Commit	Smoke test	Result
1	Open chart with PnL ≥ 1000 EUR on es-ES regional → Open PnL positive shows green, negative shows red	✅
1	Same scenario on en-US regional → no regression	✅
2	Long scroll session → no growth in GC pressure or per-frame allocations from the border pen path	✅
3	Recompile and apply → render output identical to commit 2 (no visual change expected)	✅

[Stig4all]

Reviewed and tested locally against current Develop.

The functional change looks good to me: PnL coloring now uses the raw decimal values instead of parsing formatted strings, so the culture-dependent coloring issue should be fixed. I also verified that the PR builds successfully, and all four pending PRs merge together into Develop without conflicts or build errors.

Minor non-blocking cleanup:

• _borderPen is introduced but OnRender still creates new RenderPen(Color.Gray, 1) inline.
• var old = _font; in FontSize setter is unused.
• There is a broken character in the Total PnL comment.

No blocking issues from my side. OK to merge after optional cleanup.