Remove `is_ok` and delete default constructor

[samcunliffe]

Context/Description

Explicitly delete the HDF5Base() default constructor, and remove is_ok.

More details

This should ensure we never have a nullptr file_ member. It means any HDF5{Reader,Writer} must always have a file on disk. And [claim] we never need to do health checks and nullptr checks.

Documentation

• Docs not related to this feature but I added an "idiot's" guide to running MATLAB from the CL to generate test data.

[codecov[bot]]

Codecov Report

Patch and project coverage have no change.

Comparison is base (d32dddb) 26% compared to head (12e2f1d) 26%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #332 +/- ## =================================== - Coverage 26% 26% -0% =================================== Files 71 71 Lines 3710 3707 -3 =================================== - Hits 980 977 -3 Misses 2730 2730 ``` | [Impacted Files](https://app.codecov.io/gh/UCL/TDMS/pull/332?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=UCL) | Coverage Δ | | |---|---|---| | [tdms/include/hdf5\_io/hdf5\_base.h](https://app.codecov.io/gh/UCL/TDMS/pull/332?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=UCL#diff-dGRtcy9pbmNsdWRlL2hkZjVfaW8vaGRmNV9iYXNlLmg=) | `0% <ø> (ø)` | | | [tdms/src/hdf5\_io/hdf5\_base.cpp](https://app.codecov.io/gh/UCL/TDMS/pull/332?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=UCL#diff-dGRtcy9zcmMvaGRmNV9pby9oZGY1X2Jhc2UuY3Bw) | `98% <ø> (-<1%)` | :arrow_down: |

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