Informatively throw when value is missing (#703)

### Description

otherwise very crypto errror is thrown (missing length on undefined)
#### Other changes


### Tested

new test

### How to QA

create a proposal where the jsonTransactions are missing value
### Related issues

inspired by #702

<!-- start pr-codex -->

---

## PR-Codex overview
This PR focuses on enhancing error handling in the `proposalBuilder` by
ensuring that transactions without a `value` property throw a clear
error message. Additionally, it updates the changeset mode and adds
tests to verify the new error handling.

### Detailed summary
- Changed `mode` from `"pre"` to `"exit"` in `.changeset/pre.json`.
- Added a new entry for `@celo/governance` in
`.changeset/old-badgers-invite.md`.
- Implemented error throwing for missing `tx.value` in
`packages/sdk/governance/src/proposal-builder.ts`.
- Added unit tests for missing and zero `value` cases in
`packages/sdk/governance/src/proposal-builder.test.ts`.

> ✨ Ask PR-Codex anything about this PR by commenting with `/codex {your
question}`

<!-- end pr-codex -->

Author: aaronmgdr

.changeset/old-badgers-invite.md

@@ -0,0 +1,5 @@
+---
+'@celo/governance': patch
+---
+
+Proposals missing value property now throw with understandable error message

packages/sdk/governance/src/proposal-builder.test.ts

@@ -160,6 +160,41 @@ testWithAnvilL2('ProposalBuilder', (web3) => {
         }
       `)
     })
+    it('throws error for missing value', async () => {
+      const tx = {
+        contract: 'FeeCurrencyDirectory',
+        function: 'setCurrencyConfig',
+        args: [
+          '0x765DE816845861e75A25fCA122bb6898B8B1282a',
+          '0xefB84935239dAcdecF7c5bA76d8dE40b077B7b33',
+          '50000',
+        ],
+      }
+      // @ts-expect-error (value is missing)
+      await expect(proposalBuilder.fromJsonTx(tx)).rejects.toThrowErrorMatchingInlineSnapshot(
+        `"Missing tx.value"`
+      )
+    })
+    it('successed for 0 value', async () => {
+      const tx = {
+        contract: 'FeeCurrencyDirectory',
+        function: 'setCurrencyConfig',
+        args: [
+          '0x765DE816845861e75A25fCA122bb6898B8B1282a',
+          '0xefB84935239dAcdecF7c5bA76d8dE40b077B7b33',
+          '50000',
+        ],
+        value: 0,
+      }
+      // @ts-expect-error (value is missing)
+      await expect(proposalBuilder.fromJsonTx(tx)).resolves.toMatchInlineSnapshot(`
+        {
+          "input": "0x216ab7df000000000000000000000000765de816845861e75a25fca122bb6898b8b1282a000000000000000000000000efb84935239dacdecf7c5ba76d8de40b077b7b33000000000000000000000000000000000000000000000000000000000000c350",
+          "to": "0x5a7D21C9255DAA32109c8136661D7e853Fc5BF63",
+          "value": 0,
+        }
+      `)
+    })
     it('gives info when it fails to build transaction', async () => {
       const tx = {
         contract: 'SuperContract',

packages/sdk/governance/src/proposal-builder.ts

@@ -233,6 +233,10 @@ export class ProposalBuilder {
   fromJsonTx = async (
     tx: ProposalTransactionJSON | ExternalProposalTransactionJSON
   ): Promise<ProposalTransaction> => {
+    if (tx.value === undefined) {
+      throw new Error('Missing tx.value')
+    }
+
     if (isRegistryRepoint(tx)) {
       // Update canonical registry addresses
       const args = registryRepointArgs(tx)