MtApi5: expose TesterDeposit and TesterWithdrawal for backtesting

[biohazardxxx]

Summary

Exposes the MQL5 strategy-tester money functions through the MtApi5 connector so backtesting EAs driven from .NET can simulate deposits and withdrawals. MQL5 provides TesterDeposit/TesterWithdrawal natively, but neither was reachable from the C# client.

C# client (MtApi5) — 2 methods on MtApi5Client:

Command id	Method
370	bool TesterDeposit(double money)
371	bool TesterWithdrawal(double money)

MQL5 EA (mq5/MtApi5.mq5) — Execute_TesterDeposit/Execute_TesterWithdrawal handlers + executor registrations. mq5/MtApi5.ex5 recompiled (0 errors).

TestClient — TesterDeposit/TesterWithdrawal buttons for manual exercising (hardcoded 1000.0 amount, logs the bool result).

Implementation notes

• Command ids 370/371 are identical in the C# Mt5CommandType enum and the mq5 ADD_EXECUTOR table; no collisions with existing ids.
• The C# methods send {"Money": <double>} and deserialize a JSON bool; the response path is the same proven pattern as the existing IsTesting command.
• The EA handlers call the MQL5 built-ins directly and guard with IsTesting(): outside the strategy tester they return CreateErrorResponse(-1, "... can be used only for backtesting"), exactly mirroring the existing Execute_TesterStop/Execute_UnlockTicks precedent. On the C# side that means a call outside the tester throws ExecutionException rather than returning false; inside the tester the built-in's bool result is returned. This is documented in the XML doc comments.
• TesterStatistics was deliberately not included: it is only callable from OnTester/OnDeinit, which makes it unusable over this OnTimer/OnTick RPC bridge.

Testing

• MtApi5 and MtApi5TestClient build clean in Release (MtApi5 with 0 warnings; the TestClient's 334 nullable-reference warnings are pre-existing and none are in the new code).
• MtApi5.mq5 compiles via MetaEditor with "Result: 0 errors"; the recompiled MtApi5.ex5 is included.
• Not runtime-tested: the feature has not been exercised against a live MT5 terminal / strategy tester session — verification is build/compile only.

Branch is based on dev and contains tester-money changes only; the diff is purely additive with no changes to existing behavior.

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