Migrate interp1d to FastInterpolations backend

[mgyoo86]

Summary

Move interp1d from DataInterpolations + in-house TypedInterp wrapper to the new FastInterpolations package. The zero-allocation / type-stability machinery from #85 now lives in a dedicated package, so IMASdd no longer maintains it directly.

Main Changes

• Add FastInterpolations dependency
• Migrate interp1d to use FastInterpolations API, except for :lagrange scheme

Performance Impact

1. Pure interpolation (linear, 51 grid × 1000 queries, in-place)

• ~20× faster, zero allocations.

# master
julia> @btime $itp($out, $xq);
  20.041 μs (0 allocations: 0 bytes)

# This PR
julia> @btime $itp($out, $xq);
  1.004 μs (0 allocations: 0 bytes)

2. Upstream: IMAS.trace_surfaces

• ~30% faster.

dd = IMAS.json2imas(joinpath(pkgdir(IMAS.IMASdd), "sample", "omas_sample.json"));

# master
julia> @btime IMAS.trace_surfaces(dd.equilibrium.time_slice[], IMAS.first_wall(dd.wall)...);
  535.500 μs (7769 allocations: 262.00 KiB)

# This PR
julia> @btime IMAS.trace_surfaces(dd.equilibrium.time_slice[], IMAS.first_wall(dd.wall)...);
  376.666 μs (7747 allocations: 261.58 KiB)

[codecov]

Codecov Report

❌ Patch coverage is 80.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 43.94%. Comparing base (fc5d748) to head (7f66a56).

Files with missing lines	Patch %	Lines
src/math.jl	80.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #99      +/-   ##
==========================================
- Coverage   43.95%   43.94%   -0.01%     
==========================================
  Files          15       15              
  Lines       31419    31407      -12     
==========================================
- Hits        13810    13803       -7     
+ Misses      17609    17604       -5     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.