Fix bug that can't parse materials with implicit library specification.

[MicahGale]

The material parser was built assuming that all isotope specifications required a library, e.g., 1001.80c. However according to the 6.2 manual table 3-32:

Either a full ZZZAAA.abx or partial ZZZAAA element or nuclide
identifier for each constituent i, where ...

Therefore, this assumption is flawed.

To fix this, a dedicated MaterialParser was created. 1001 is ambiguous if it is part of a number sequence or a ZAID. So this parser just accepts both Isotopes and number sequences as valid. This avoids the need of contextual parser with a look-ahead capability by making the input contextual as an input level.

@SterlingButters you can review this if you like, but you don't need to.

As for the specific error message that was found in #365. The Material assumed it had an IsotopesNode which is a list of tuples, and was given a ListNode instead. It tried to unpack the ValueNode inside the list like a tuple, and freaked out.

Fixes #365.

[MicahGale]

This needs to wait until #336 is merged due to the de facto deployment freeze depending on that.

[coveralls]

Pull Request Test Coverage Report for Build 8695235312

Details

• 47 of 47 (100.0%) changed or added relevant lines in 4 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.01%) to 98.138%

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Totals
Change from base Build 8694707289:	0.01%
Covered Lines:	5744
Relevant Lines:	5853

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💛 - Coveralls

[MicahGale]

Thank you!