GeezerVison

Reduce repeated field inversions in ShamirSplitSecret.getSecret() and divide(), preserving the existing API.

• Accumulate interpolation numerator and denominator products, then invert once per coefficient: 16,256 to 128 inversions for 128 shares.
• Reuse one inverse per eligible share row: 256 to 8 inversions for eight 32-byte shares.
• Keep the original behavior for Polynomial subclasses and small inputs.
• Add scaling and overridden-division regression tests to the threshold suite.

Verification at upstream e40316b:

• 16 threshold JUnit tests pass on Java 17 with --release 8.
• Both new subclass regressions fail on the unguarded optimization and pass on upstream original and this candidate.
• All 1,594 differential probe outputs match original, Sandbox-generated and candidate source.
• With -Xlint:all -Xmaxwarns 10000, both builds report the same 101 existing warnings; no added diagnostics in the threshold test closure.
• git diff --check passes.

The full Gradle/core suite, Checkstyle and JMH were not run for this submission. Counts above refer to field inversions, not a measured runtime speedup.

Identified by the Sandbox mathematics cleanup:
https://github.com/carstenartur/sandbox
Sandbox qualification:
https://github.com/carstenartur/sandbox/actions/runs/42453057191/job/128646172609

Generated source was adapted for naming, comments and formatting while preserving its guards, masks, fallback paths and per-row schedule. ChatGPT assisted with preparation, regression tests and review.