Pin the packages to the rc5 preview - #298

Stacked on #289. Hold: don't merge until the pin is moved to the v0.3.0-rc.5 tag.

Pins all four packages to ed05cfe on the rc5-preview (lambda-feedback/lambda-feedback-packages#15) branch of lambda-feedback-packages. That branch is v0.3.0-rc.4 (#280 is already on it: units was renamed physical_quantities) with these merged in:

• expression-parsing: big-operator task symbols wrap their argument lambda-feedback-packages#11: big-operator task symbols (from Fix/sum preview #261)
• expression-parsing: add read_written_number for significant figures and decimal places lambda-feedback-packages#12: read_written_number for significant figures and decimal places (from Add support for significant figures (sig_figs) parameter #273 and Add decimal_places grading parameters #277)
• expression-parsing: parse inequalities, != and chained equalities lambda-feedback-packages#13: inequalities, != and chained equalities (from Support inequalities in the answer and response #276 and Support chained equalities in the answer and response #278)

The app ports of those PRs stack on this one, so they can be tested against the package code before rc5 is tagged.

Expected failures

• test_radians_to_frequency: a known failure, which also fails on main.
• The a!=b cases in test_exclamation_mark_for_factorial and test_double_exclamation_mark_for_factorial. != now parses as Ne(a, b), where it used to be read as factorial(a) = b, and check_equality raises TypeError when it subtracts an Unequality. The Support inequalities in the answer and response #276 port, stacked above this PR, fixes them; there's deliberately no stopgap here.

Before merging

• Tag v0.3.0-rc.5 and pin to it, instead of the SHA.
• Update the package version in README.md (which still says rc.2) and app/docs/dev.md (which says rc.4).

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