chore(builder): add unit tests to bundle_sender

[dancoombs]

Create a unit testing framework for bundle_sender and write some tests.

[0xfourzerofour]

Looks good, solid testing cases as well

[codecov]

Codecov Report

Attention: Patch coverage is 93.53846% with 42 lines in your changes missing coverage. Please review.

Project coverage is 57.15%. Comparing base (e94744a) to head (d5abafe).

Additional details and impacted files

Files	Coverage Δ
crates/builder/src/bundle_proposer.rs	90.37% <100.00%> (+4.16%)	⬆️
crates/builder/src/transaction_tracker.rs	81.17% <100.00%> (+0.03%)	⬆️
crates/builder/src/bundle_sender.rs	72.80% <92.30%> (+72.80%)	⬆️

... and 2 files with indirect coverage changes

Flag	Coverage Δ
unit-tests	57.15% <93.53%> (+2.72%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Components	Coverage Δ
rundler binary	0.00% <ø> (ø)
builder	59.54% <93.53%> (+14.01%)	⬆️
dev	0.00% <ø> (ø)
pool	65.07% <ø> (ø)
provider	16.10% <ø> (ø)
rpc	25.66% <ø> (ø)
sim	78.13% <ø> (+0.26%)	⬆️
tasks	∅ <ø> (∅)
types	65.45% <ø> (ø)
utils	18.28% <ø> (ø)