Allow parsing of EC public keys, get format

[justsmth]

Issues:

Resolves #ISSUE-NUMBER1
Addresses #ISSUE-NUMBER2

Description of changes:

Describe current behavior and how your code changes that behavior. If there are no issues this pr is resolving, explain why this change is necessary.

Call-outs:

Point out areas that need special attention or support during the review process. Discuss architecture or design changes.

Testing:

How is this change tested (unit tests, fuzz tests, etc.)? Are there any testing steps to be verified by the reviewer?

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

Attention: Patch coverage is 80.55556% with 35 lines in your changes missing coverage. Please review.

Project coverage is 92.30%. Comparing base (c358484) to head (e79faab).
Report is 78 commits behind head on main.

Files with missing lines	Patch %	Lines
aws-lc-rs/src/agreement.rs	72.50%	19 Missing and 3 partials ⚠️
aws-lc-rs/src/ec.rs	86.45%	11 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #519      +/-   ##
==========================================
- Coverage   95.80%   92.30%   -3.50%     
==========================================
  Files          61       67       +6     
  Lines        8143     9352    +1209     
  Branches        0     9352    +9352     
==========================================
+ Hits         7801     8632     +831     
- Misses        342      448     +106     
- Partials        0      272     +272     

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