fix: replace misleading error messages in key fetching

[luchobonatti]

Closes zama-ai#379

Summary

• Replace catch-all "Impossible to fetch public key: wrong relayer url." with neutral, resource-specific messages using TFHEError
• Original cause.message is now auto-surfaced as Details: via RelayerErrorBase, fixing the problem of environments that don't support Error.cause

Changes

File	Change
src/relayer-provider/v1/networkV1.ts	Use TFHEError with "Failed to fetch keys from relayer"
src/sdk/lowlevel/TFHEPublicKey.ts	Message → "Failed to fetch public key"
src/sdk/lowlevel/TFHEPkeCrs.ts	Message → "Failed to fetch CRS"
src/sdk/lowlevel/TFHEPkeParams.ts	Message → "Failed to fetch PKE params"
src/sdk/lowlevel/TFHEPublicKey.test.ts	Update 3 assertions
src/sdk/lowlevel/TFHEPkeCrs.test.ts	Update 3 assertions
src/sdk/lowlevel/TFHEPkeParams.test.ts	Update 2 assertions

Test plan

• prettier:check passes
• eslint passes
• 87 tests pass across 4 affected suites

[Copilot]

Pull request overview

This PR updates key-fetching error messages to be neutral and resource-specific, replacing a misleading catch-all message and standardizing errors around TFHEError so underlying causes surface consistently.

Changes:

• Replaced the generic “wrong relayer url” message with resource-specific messages for public key / CRS / PKE params fetches.
• Switched getKeysFromRelayer to throw TFHEError with a neutral “Failed to fetch keys from relayer” message.
• Updated affected unit tests to assert the new messages.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/relayer-provider/v1/networkV1.ts	Wrap key-fetch failures in TFHEError with a neutral message.
src/sdk/lowlevel/TFHEPublicKey.ts	Update fetch wrapper message to “Failed to fetch public key”.
src/sdk/lowlevel/TFHEPkeCrs.ts	Update fetch wrapper message to “Failed to fetch CRS”.
src/sdk/lowlevel/TFHEPkeParams.ts	Update fetch wrapper message to “Failed to fetch PKE params”.
src/sdk/lowlevel/TFHEPublicKey.test.ts	Update assertions to match the new public key fetch error message.
src/sdk/lowlevel/TFHEPkeCrs.test.ts	Update assertions to match the new CRS fetch error message.
src/sdk/lowlevel/TFHEPkeParams.test.ts	Update assertions to match the new PKE params fetch error message.

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