python-v2: add svm mechanism

[phdargen]

Description

Adds svm mechanism to python v2 sdk. Closely follows ts implementation with inspiration from #607 by @HealthyBuilder for python specifics

Tests

• added unit tests, all pass
• added integration tests, all pass
• added e2e test
• manual test: updated server examples

📊 Test Summary
==============
✅ Passed: 3
❌ Failed: 0
📈 Total: 3

📋 Detailed Test Results
========================

✅ PASSED TESTS:

  # 1: httpx → fastapi → /protected-svm
      Facilitator: typescript | Network: solana:EtWTRABZaYq6iMfeYKouRu166VU2xqa1 | Tx: 3VG4HiztbB...
  # 2: requests → fastapi → /protected-svm
      Facilitator: typescript | Network: solana:EtWTRABZaYq6iMfeYKouRu166VU2xqa1 | Tx: 3rGRez1LyS...
  # 3: httpx → flask → /protected-svm
      Facilitator: typescript | Network: solana:EtWTRABZaYq6iMfeYKouRu166VU2xqa1 | Tx: 5z4HD5M5SW...

📊 Breakdown by Facilitator:
   typescript      ✅ 3 / ❌ 0 (100%)

📊 Breakdown by Server:
   fastapi              ✅ 2 / ❌ 0 (100%)
   flask                ✅ 1 / ❌ 0 (100%)

📊 Breakdown by Client:
   httpx                ✅ 2 / ❌ 0 (100%)
   requests             ✅ 1 / ❌ 0 (100%)

Flask server + httpx client:

Response status: 200
Response body: {"report":{"temperature":70,"weather":"sunny"}}

Payment response: {
  "success": true,
  "error_reason": null,
  "payer": "0xE33A295AF5C90A0649DFBECfDf9D604789B892e2",
  "transaction": "0x28ef7b73666b63fa0e9e1f75b21c9651a170a96a6c672987f990baa2c4d4b99c",
  "network": "eip155:84532"
}

Checklist

• I have formatted and linted my code
• All new and existing tests pass
• My commits are signed (required for merge) -- you may need to rebase if you initially pushed unsigned commits

[vercel]

@phdargen is attempting to deploy a commit to the Coinbase Team on Vercel.

A member of the Team first needs to authorize it.

[CarsonRoscoe]

Great work @phdargen!

Now that #901 is merged, could we add the EVM/SVM dependencies as optional extras?

[phdargen]

Great work @phdargen!

Now that #901 is merged, could we add the EVM/SVM dependencies as optional extras?

Done @CarsonRoscoe, also updated the server/client examples to use the new import pattern