Use Mazur-bound small-multiple torsion check in rank search

[asiryan]

Motivation

• The rank lower-bound search used a heavy torsion-filter 5040*P scalar multiplication which can be very expensive and may cause the example to hang for curves with positive rank.
• Over Q, Mazur’s theorem bounds torsion orders ≤ 16; a small-multiple check up to 16 is sufficient to detect torsion while avoiding large scalar multiplications.
• Replace the expensive global multiplier with a lightweight check to improve responsiveness of RankLowerBoundFromSearch for typical inputs.
• Keep the bound conservative and still correct for torsion detection over Q.

Description

• Replaced the previous torsionKiller = 5040 approach in RankLowerBoundFromSearch with a direct call to a new helper IsTorsionByMazurBound.
• Added IsTorsionByMazurBound(EllipticCurvePoint) which tests whether a point is torsion by checking multiples k*P for 1..16 and returns true when a multiple is the point at infinity.
• Updated comments to document that torsion orders over Q are ≤ 16, and removed the large constant and its usage.
• Changes are localized to sources/EllipticCurveQ.Analysis.cs and only affect the torsion filtering step of the rational-point search used for rank lower bounds.

Testing

• Attempted to run the example via dotnet run --project /workspace/EllipticCurves/examples; automated run failed because dotnet is not available in the environment.
• No other automated tests were executed in this environment.
• Static/compile-time checks were not performed here due to lack of build tooling in the sandbox.

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Codex Task