fix: correctly export PickupRecipientMessageHandler

[nickreynolds]

What issue is this PR fixing

Recent DIDComm Mediator work was actually missing 2 exports :)

Quality

Check all that apply:

• I want these changes to be integrated
• I successfully ran pnpm i, pnpm build, pnpm test, pnpm test:browser locally.
• I allow my PR to be updated by the reviewers (to speed up the review process).
• I added unit tests.
• I added integration tests.
• I did not add automated tests because _________, and I am aware that a PR without tests will likely get rejected.

[codecov]

Codecov Report

Base: 80.25% // Head: 84.65% // Increases project coverage by +4.40% 🎉

Coverage data is based on head (11ee872) compared to base (125bf42).
Patch coverage: 81.35% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##             next    #1121      +/-   ##
==========================================
+ Coverage   80.25%   84.65%   +4.40%     
==========================================
  Files         118      145      +27     
  Lines        4056    14801   +10745     
  Branches      875     1548     +673     
==========================================
+ Hits         3255    12530    +9275     
- Misses        798     2271    +1473     
+ Partials        3        0       -3     

Impacted Files	Coverage Δ
packages/core-types/src/agent.ts	0.00% <0.00%> (ø)
packages/core-types/src/coreEvents.ts	0.00% <ø> (ø)
packages/core-types/src/index.ts	0.00% <0.00%> (ø)
...s/credential-ld/src/module-types/jsonld/index.d.ts	0.00% <0.00%> (ø)
packages/data-store-json/src/types.ts	0.00% <0.00%> (ø)
...ackages/did-provider-ethr/src/ethr-did-provider.ts	87.09% <ø> (+3.76%)	⬆️
packages/did-provider-ethr/src/index.ts	100.00% <ø> (ø)
packages/did-provider-ethr/src/kms-eth-signer.ts	69.73% <ø> (-8.05%)	⬇️
packages/did-provider-ion/src/functions.ts	95.68% <ø> (ø)
packages/did-provider-ion/src/index.ts	100.00% <ø> (ø)
... and 215 more

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[mirceanis]

Looks good