nanoql 2.1

Added

• The C++ layer: each platform's C archive carries nanoql.hpp, C++17 over nanoql.h, and a CMake package in
  lib/cmake/nanoql/: find_package(nanoql CONFIG) gives nanoql::cpp and nanoql::c, and a version request
  follows CMake's SameMajorVersion rule. The C++ page covers installing, CMake and a first program
  (#7).
• nanoql-bind writes the C++ layer for a library of your own: cpp, and build's include/ beside the C
  headers.
• Migrating from QuantLib's C++: a guide pairs QuantLib's C++ with nanoql's
  C++ layer for the rates products, beside the QuantLib-Python and QLNet guides.

Fixed

• Python: OISRateHelper's tenor form and SwapRateHelper's two forms taking a rate can be called without
  forward_start or fwd_start, as their defaults allow; they raised "no overload takes these arguments" (#8).

Validation

• The coverage figures count only the lines a test executes: the test data the runner built while discovering the
  tests no longer counts as covered, so the same tests read slightly lower figures than 2.0's.

Known limits

• The Excel add-ins are unsigned. A firm whose Excel requires add-ins signed by a trusted publisher signs the .xll
  with its own certificate.
• The add-ins run on the .NET 10 Desktop Runtime, Excel-DNA's just-in-time path, not compiled to native code.
• The bindings, the C++ layer among them, cover Windows x64 and Linux x64 (glibc 2.28 or later); Windows Arm64,
  Linux Arm64 and macOS on Apple silicon follow in later releases, and Intel Macs have none, though nanoql's .NET
  library runs there.
• Python 3.11 or later.
• The Java layer is built and tested in the repository and not released.

The platforms in this release's run

• Windows x64: 8,622 of 8,622 tests pass, the reference platform.
• Linux x64: 8,549 of 8,622 tests pass; 73 fail, reported and not blocking: NanoQL.Tests.Conventions.HestonSlvMcQualityMaximumTests.TheCalibrationsLargestErrorIsWithinFifteenBasisPoints, NanoQL.Tests.Divergences.AbcdCalibrationGuardTests.TheFitsQuantLibCompletesKeepItsBits(set: 5, a: 0.45336334464724903, b: -1.4254877636528123, c: 1.5935876342523034, d: 0.26597942707915356), NanoQL.Tests.Divergences.CalibrationBasketNominalTests.AFlippedSolutionKeepsItsNominal, NanoQL.Tests.Divergences.CirFellerConstraintTests.ACalibrationWithTheSpeedAndLevelFixedIsQuantLibs, NanoQL.Tests.Divergences.CmsCalibrationGuessTests.TheFixedPathStartsAtTheGuess, NanoQL.Tests.Divergences.CmsCalibrationReversionTransformTests.TheLevenbergMarquardtFitsKeepQuantLibsValues, NanoQL.Tests.Divergences.CmsCalibrationReversionTransformTests.TheSimplexFitsHaveAFiniteReversion, NanoQL.Tests.Divergences.CrossCurrencySwapCompoundedSpreadFairSpreadTests.TheBasisSwapsCompoundingLegsFairSpreadIsSolved, NanoQL.Tests.Divergences.CrossCurrencySwapCompoundedSpreadFairSpreadTests.TheFixedVsFloatingSwapsCompoundingLegsFairSpreadIsSolved, NanoQL.Tests.Divergences.CrossCurrencySwapCompoundedSpreadFairSpreadTests.TheMtMSwapsCompoundingLegsFairSpreadIsSolved and 63 more.
• macOS Arm64: 8,546 of 8,622 tests pass; 76 fail, reported and not blocking: NanoQL.Tests.Conventions.BoostSignTests.TheSignOfANaNIsItsSignBit, NanoQL.Tests.Divergences.AbcdCalibrationGuardTests.TheFitsQuantLibCompletesKeepItsBits(set: 5, a: 0.45336334464724903, b: -1.4254877636528123, c: 1.5935876342523034, d: 0.26597942707915356), NanoQL.Tests.Divergences.BetaRiskTests.AMultiEventPathMovesItsLaterDatesOnly, NanoQL.Tests.Divergences.CTSMMCapletAlphaFormCalibrationTests.ACalibrationWhoseReturnedPassFitsKeepsQuantLibsNumbers, NanoQL.Tests.Divergences.CalibrationBasketNominalTests.AFlippedSolutionKeepsItsNominal, NanoQL.Tests.Divergences.CirFellerConstraintTests.ACalibrationWithTheSpeedAndLevelFixedIsQuantLibs, NanoQL.Tests.Divergences.CmsCalibrationGuessTests.TheFixedPathStartsAtTheGuess, NanoQL.Tests.Divergences.CmsCalibrationReversionTransformTests.TheLevenbergMarquardtFitsKeepQuantLibsValues, NanoQL.Tests.Divergences.CmsCalibrationReversionTransformTests.TheSimplexFitsHaveAFiniteReversion, NanoQL.Tests.Divergences.CrossCurrencySwapCompoundedSpreadFairSpreadTests.TheBasisSwapsCompoundingLegsFairSpreadIsSolved and 66 more.
• The linux-x64 bindings: every check green.
• The win-x64 bindings: every check green.