[UUM-133527] - Improve floating point precision when Probuilderizing small objects

[thomas-tu]

DO NOT FORGET TO INCLUDE A CHANGELOG ENTRY

Purpose of this PR

[Brief summary of the changes in this PR.]

Links

Jira: https://jira.unity3d.com/browse/UUM-133527

Comments to Reviewers

[List known issues, planned work, provide any extra context for your code.]

[u-pr]

The review identified a critical issue regarding the increase of FltCompareResolution. This change is likely to cause integer overflows and floating-point stability issues.

_{🤖 Helpful? 👍/👎}

[u-pr]

Have you considered the impact of this new resolution on float precision limits and potential integer overflows?

Increasing FltCompareResolution to 1000000f introduces two major issues:

1. Integer Overflow: Conversions in VectorHash and related structs (like IntVec3) multiply vertex coordinates by this resolution and convert them using System.Convert.ToInt32(). With a multiplier of 1,000,000, any coordinate with a magnitude greater than ~2147.48 will exceed int.MaxValue, triggering a runtime OverflowException and crashing the mesh generation process.
2. Hash Stability: The purpose of this resolution is to mask floating-point imprecision so that spatially identical vertices hash to the same value. A 32-bit float only provides ~7 significant decimal digits. A scale of 1,000,000 demands exactness up to $10^{-6}$. For any coordinate $\ge 10$, this exceeds standard float precision limits. Minor math inaccuracies will cause virtually identical vertices to resolve to different integers, which will break vertex welding, duplicate detection, and spatial sorting.

I highly recommend reverting this to 1000f (which provides a reliable $0.001$ precision tolerance and safely supports coordinates up to ~2,000,000) to maintain tool stability.

_{🤖 Helpful? 👍/👎}

[codecov-github-com]

Codecov Report

All modified and coverable lines are covered by tests ✅

@@           Coverage Diff           @@
##           master     #658   +/-   ##
=======================================
  Coverage   36.05%   36.06%           
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  Files         277      277           
  Lines       34909    34910    +1     
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+ Hits        12588    12589    +1     
  Misses      22321    22321           

Flag	Coverage Δ
probuilder_MacOS_6000.0	34.58% <ø> (ø)
probuilder_MacOS_6000.3	34.58% <ø> (ø)
probuilder_MacOS_6000.4	34.57% <ø> (ø)
probuilder_MacOS_6000.5	34.58% <ø> (+<0.01%)	⬆️
probuilder_MacOS_6000.6	34.57% <ø> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
Runtime/Core/VectorHash.cs	100.00% <ø> (ø)

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