Add Betasampler

[codecov[bot]]

Codecov Report

Patch coverage: 81.08% and project coverage change: +29.00 :tada:

Comparison is base (a334953) 30.05% compared to head (f703cb8) 59.05%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #202 +/- ## =========================================== + Coverage 30.05% 59.05% +29.00% =========================================== Files 15 15 Lines 985 1016 +31 =========================================== + Hits 296 600 +304 + Misses 689 416 -273 ``` | [Impacted Files](https://app.codecov.io/gh/YichengDWu/Sophon.jl/pull/202?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Yicheng+Wu) | Coverage Δ | | |---|---|---| | [src/Sophon.jl](https://app.codecov.io/gh/YichengDWu/Sophon.jl/pull/202?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Yicheng+Wu#diff-c3JjL1NvcGhvbi5qbA==) | `100.00% <ø> (ø)` | | | [src/pde/discretize.jl](https://app.codecov.io/gh/YichengDWu/Sophon.jl/pull/202?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Yicheng+Wu#diff-c3JjL3BkZS9kaXNjcmV0aXplLmps) | `36.66% <50.00%> (+36.66%)` | :arrow_up: | | [src/pde/utils.jl](https://app.codecov.io/gh/YichengDWu/Sophon.jl/pull/202?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Yicheng+Wu#diff-c3JjL3BkZS91dGlscy5qbA==) | `38.88% <66.66%> (+38.88%)` | :arrow_up: | | [src/pde/pinnsampler.jl](https://app.codecov.io/gh/YichengDWu/Sophon.jl/pull/202?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Yicheng+Wu#diff-c3JjL3BkZS9waW5uc2FtcGxlci5qbA==) | `17.50% <84.00%> (+17.50%)` | :arrow_up: | | [src/pde/sym\_utils.jl](https://app.codecov.io/gh/YichengDWu/Sophon.jl/pull/202?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Yicheng+Wu#diff-c3JjL3BkZS9zeW1fdXRpbHMuamw=) | `81.92% <100.00%> (+81.92%)` | :arrow_up: | ... and [3 files with indirect coverage changes](https://app.codecov.io/gh/YichengDWu/Sophon.jl/pull/202/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Yicheng+Wu)

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