Keep AWS-LC's post-quantum defaults unless the policy opts out

[WillChilds-Klein]

Stack, split out of #3442, to merge bottom-up:

1. Add ERR_num_errors and ERR_pop_to_count #3501 -- error-queue primitives
2. Add a reader for the system crypto-policies OpenSSL back-end #3502 -- policy file reader
3. Seed cipher lists and version bounds from the system crypto policy #3503 -- cipher lists and version bounds
4. Seed groups and signature algorithms from the system crypto policy #3504 -- groups and signature algorithms
5. Keep AWS-LC's post-quantum defaults unless the policy opts out #3505 -- post-quantum defaults (this PR)

Description

• Keeps AWS-LC's post-quantum defaults when the policy says nothing about them. Every policy the framework ships today predates ML-KEM and ML-DSA, and the setters replace AWS-LC's defaults rather than intersect with them, so seeding downgraded every context.
• A policy that names any post-quantum algorithm is taken at its word and nothing is added back.
• A hybrid group returns only where the policy keeps its classical half, so a policy without secp384r1 has no SecP384r1MLKEM1024 either, and a group the policy removes with - stays out.
• Turning post-quantum off wholesale takes a directive of AWS-LC's own, AWSLC.PostQuantum = off, since nothing the framework writes says "no post-quantum". Other readers of the file ignore an unknown key.
• The groups to restore are derived from AWS-LC's own defaults at runtime, so they follow any change to them.

Testing / verification

• Tests cover both directions: a silent policy keeps the post-quantum entries, and a policy naming one is left as written.
• The opt-out is checked case-insensitively, and other values of the directive are checked to keep the defaults.
• The hybrid rule is exercised by a policy that keeps one classical curve and drops another, and by one that removes a hybrid outright.
• The framework's hyphenated spellings, such as x25519-mlkem768 and ml-dsa-65, are checked to resolve to AWS-LC's ids.
• Each guard was checked by neutering it in turn, including the opt-out, the check that a policy naming post-quantum is authoritative, and the classical-half requirement.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license and the ISC license.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
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Additional details and impacted files

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