Implement a local transaction simulation layer using Soroban's simulation RPC

[Kingsman-99]

Overview

Before submitting any transaction, the SDK should optionally simulate it against the Soroban RPC to get fee estimates, resource usage, and detect errors — without consuming sequence numbers or broadcasting. Add a simulate option to all mutating SDK methods.

Requirements

• Add { simulate: true } option to createInvoice, pay, release, refund, approveRelease
• When simulate: true, call simulateTransaction RPC instead of submitting
• Return SimulationResult { success: boolean, error?: string, fee: bigint, cpuInsns: bigint, memBytes: bigint, footprint: LedgerFootprint }
• Add client.simulate(method, params) generic simulation method
• Write tests using a mock RPC that returns simulation responses
• Document simulation usage in README.md with a code example

Acceptance Criteria

• simulate option works on all 5 mutating methods
• SimulationResult type exported from package
• Generic client.simulate() method works
• README.md updated with simulation example
• All existing tests pass
• npm test passes with zero failures
• TypeScript compiles with zero errors
• ESLint passes with zero errors

Definition of Done

All CI checks must pass before the PR is reviewed.

[nurudeenheroic]

Hi! I've gone through the issue and understand what's required. I'm confident I can deliver an efficient solution that meets the expectations.

[zeemscript]

Hello @maintainer, I’ve gone through the requirements and I’m confident I can implement a proper solution that matches the acceptance criteria. Kindly assign this issue to me.

[levibliz]

I have relevant experience with this area and would like to work on this issue. Kindly assign it to me.

[grantfox-oss]

🦊 GrantFox — @levibliz has been assigned to this issue as part of the Official Campaign | FWC26 campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #421)
2. Your PR will be reviewed by the Stellar-split maintainers

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