fix: round interpolated texture tile sizes

[banteg]

Summary

This fixes interpolated texture tile dimensions being truncated after uls/ult/lrs/lrt interpolation.

The bug showed up on macOS/Apple Silicon as animated water/lava textures visibly jittering when interpolation is active. In the Fire Temple lava repro, one replay phase derived a different rendered texture window from the interpolated tile coordinates:

replay=1
tile0=(0.000,6.333,124.000,130.333)
renderSize0=(32, 31)
texSize0=(32, 31)

Adjacent phases for the same surface stayed 32x32, so the visible symptom was an alternating 32x32 / 32x31 texture window.

replay0=(0.000,6.000,124.000,130.000) renderSize0=(32, 32)
replay1=(0.000,6.333,124.000,130.333) renderSize0=(32, 31) # bugged!
replay2=(0.000,6.667,124.000,130.667) renderSize0=(32, 32)

Root Cause

Several paths in src/fast/interpreter.cpp derive rendered/imported tile dimensions with:

(high - low + 4) / 4

Those results were then cast directly to integer types. With interpolated float coordinates, a texel count that is logically 32.0 can land slightly below the integer boundary, so truncation turns it into 31.

That makes the texture clamp/import and draw-time texture size calculations disagree across interpolation phases, producing the observed water/lava animation jitter.

Fix

Add GetTileSizeFromCoordinates() and use it for the tile-size calculations that derive dimensions from interpolated tile coordinates. It keeps non-positive sizes clamped to 0 and rounds the derived texel count with lroundf.

Related Links

• Fixes Interpolated texture tile sizes can truncate and cause water/lava jitter #1119
• Shipwright report: [Graphical Bug, Nightly] Texture Animations render incorrectly on non-20 fps HarbourMasters/Shipwright#6666

Validation

• cmake -S . -B build -DLUS_BUILD_TESTS=OFF
• cmake --build build --target libultraship -j 8
• cmake -S . -B build -DLUS_BUILD_TESTS=ON
• cmake --build build --target lus_tests -j 8
• ctest --test-dir build --output-on-failure