perf(nad): expose geometryPrecision as a viewer parameter

[gautierbureau]

Context

Follow-up to the geometry-precision PR (#8), and based on its branch (claude/perf-nad-writer-geometry-precision) — not on the powsybl#423 base — because it consumes the geometryPrecision writer option that #8 introduces. Review/merge #8 first.

What

#8 added geometryPrecision to the SVG-writer options but left the viewer to pass it. This PR does that end-to-end wiring so a consumer can set it once through the public viewer parameters:

new NetworkAreaDiagramViewer(container, svg, metadata, svgMetadata, {
    createSvgFromMetadata: true,
    geometryPrecision: 1, // fewer coordinate decimals → smaller, faster SVG
});

• Adds geometryPrecision?: number to NadViewerParametersOptions (already exported, so it's public).
• NadViewerParameters.getGeometryPrecision() returns the configured value or undefined.
• Both new SvgWriter(...) sites in network-area-diagram-viewer.ts — the initial empty-SVG build and the adaptive-zoom redraw — forward it.

undefined leaves the writer on its default precision (2), so behaviour is unchanged unless a consumer opts in. The getter returns undefined rather than a hard-coded 2 to avoid duplicating the default (and a circular import with diagram-utils); the writer owns the default.

Measured impact

This PR is pure plumbing — a single optional-field read per writer construction, no runtime cost of its own. Its value is making #8's savings reachable through the public viewer API. The payoff is #8's, measured on case1354pegase:

viewer geometryPrecision	gzip SVG	vs default
unset / 2 (default)	168.5 KB	—
1	156.0 KB	−7.4%
0	140.8 KB	−16.4%

(Full raw+gzip table and methodology in #8.)

Tests

• getGeometryPrecision returns undefined when unset (both undefined and {} options) and the configured value otherwise.
• Combined with perf(nad): configurable geometry precision in the client SVG writer #8's writer test (which proves the writer honours the option), the parameter → writer path is covered.

Draft; its base is #8's branch. Once #8 merges into integration/nad_create_svg_adaptive_zoom, retarget this PR's base to that branch.

🤖 Generated with Claude Code