Implement default_sampling_points seriously

[terasakisatoshi]

On Ubuntu, Eigen::Tensor<ComplexF64, 4> gtau = tau_sampling->evaluate(gl, dim); causes an error.

-- Extracted package version: 0.1.0
-- The CXX compiler identification is GNU 13.3.0
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: /usr/bin/c++ - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Performing Test CMAKE_HAVE_LIBC_PTHREAD
-- Performing Test CMAKE_HAVE_LIBC_PTHREAD - Success
-- Found Threads: TRUE  
-- Extracted package version: 0.6.0
-- Configuring done (1.8s)
-- Generating done (0.0s)
-- Build files have been written to: /workspaces/libsparseir/build
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Randomness seeded to: 1823977355
Warning: Basis cutoff is 2.22045e-16, which is below √ε with ε = DDouble(2.4651903288156619e-32,0.0000000000000000e+00).
Expect singular values and basis functions for large l to have lower precision than the cutoff.
Warning: Basis cutoff is 1e-08, which is below √ε with ε = 2.22045e-16.
Expect singular values and basis functions for large l to have lower precision than the cutoff.
Warning: Basis cutoff is 1e-20, which is below √ε with ε = 2.22045e-16.
Expect singular values and basis functions for large l to have lower precision than the cutoff.
Warning: Basis cutoff is 1e-10, which is below √ε with ε = 2.22045e-16.
Expect singular values and basis functions for large l to have lower precision than the cutoff.
Warning: Basis cutoff is 1e-100, which is below √ε with ε = DDouble(2.4651903288156619e-32,0.0000000000000000e+00).
Expect singular values and basis functions for large l to have lower precision than the cutoff.
Warning: Basis cutoff is 1e-100, which is below √ε with ε = DDouble(2.4651903288156619e-32,0.0000000000000000e+00).
Expect singular values and basis functions for large l to have lower precision than the cutoff.
Warning: Basis cutoff is 1e-15, which is below √ε with ε = DDouble(2.4651903288156619e-32,0.0000000000000000e+00).
Expect singular values and basis functions for large l to have lower precision than the cutoff.
Warning: Expected 19 sampling points, got 34.
free(): invalid size

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
libsparseirtests is a Catch2 v3.4.0 host application.
Run with -? for options

-------------------------------------------------------------------------------
Sampling Tests
  Testing with Λ=10.000000
-------------------------------------------------------------------------------
/workspaces/libsparseir/test/sampling.cxx:23
...............................................................................

/workspaces/libsparseir/test/sampling.cxx:23: FAILED:
  {Unknown expression after the reported line}
due to a fatal error condition:
  SIGABRT - Abort (abnormal termination) signal

===============================================================================
test cases:   56 |   55 passed | 1 failed
assertions: 3401 | 3400 passed | 1 failed

run.sh: line 1:  2822 Aborted                 ./build/test/libsparseirtests

[terasakisatoshi]

Ref #98

[terasakisatoshi]

#100 fixed the issue.