fix Issue 13300 - pure function 'std.array.Appender!(T[]).Appender.ensureAddable' cannot call impure function 'test.T.__fieldPostBlit'
mark toHash as public
Merge pull request #2439 from 9rnsr/fix13300

[REG2.067a] Issue 13300 - pure function 'std.array.Appender!(T[]).Appender.ensureAddable' cannot call impure function 'test.T.__fieldPostBlit'
Fix Issue 12733 - parallelism.amap incorrect assignment without initialization
Make std.file.getTimes safe
Merge pull request #2161 from monarchdodra/parallelism

Fix Issue 12733 - parallelism.amap incorrect assignment without initiali...
Merge pull request #2446 from tom-tan/safe-file-getTimes

Make std.file.getTimes safe
Merge pull request #2456 from IgorStepanov/newaa-bigint-public-toHash

[new AA] mark toHash as public
Add `std.internal.cstring` module.
Replace most `toStringz`/`toUTF16z`/`toUTFz` usages with `tempCString*` ones.

Only non-trivial cases left when a refactoring is required to use a temporary buffer.
Also add `nothrow`/`@nogc` attributes.