Fixes for w_ipa run_calculation and reading filenames from h5 file

[SHZ66]

Issue Number. Is this pull request related to any outstanding issues? If so, list the issue number.

Describe the changes made. A clear and concise description of what the problem is and what you did to fix it. E.g. [...] was happening and I've changed [...] to fix it.

Goals and Outstanding Issues. A clear and concise list of goals (to be) accomplished.

• Fixed a bug where bytes is not properly converted into strwhen reading filenames for basis state files from west.h5.
• FIxed a bug where bootstrapping length is inaccurately calculated causing w_ipa to crash. Note that bootstrap_length is only useful for logging purposes so this change would not lead to any actual result changes.

Major files changed.

• Please see file changed section.

Status.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• I have read the CONTRIBUTING document.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.

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